Archive of Our Own ^beta

Chapter Text

It had been a little over a year since the Barrier broke.

Since Frisk walked forward with mercy in their hands and monsters trailing behind them, blinking in the light of the surface for the first time in centuries. A year since they’d stayed—not because they had to, but because they chose to. A year since humans were forced to reckon with the truth: monsters were real, monsters were here, and monsters meant no harm.

That didn’t mean everything was perfect.

Rights still had to be fought for. Laws rewritten. Equal pay remained an uphill battle no matter how much gold was worth on the surface—and it turned out, gold was very, very valuable. Currency wasn't the problem. Prejudice was.

But on this slow golden afternoon, in a small worn-down house tucked between concrete and cold wind, none of that mattered. Not for a little while.

Frisk lay sprawled across the floor in front of the television, their socked feet rhythmically kicking at the air. One hand propped up their chin while the other toyed with the fringed edge of the rug, the soft buzz of the television washing over them like a tide. Papyrus was parallel to them on the floor, lanky limbs folded in awkward angles, mimicking their pose with an earnestness that made Sans’ grin twitch just a little wider.

“YOU MUST BE AT MAXIMUM RELAXATION, HUMAN,” Papyrus declared dramatically, pointing at the screen with a flourish. “IT IS ESSENTIAL FOR ABSORBING THE OPTIMAL AMOUNT OF METTATON!”

Frisk didn’t respond with words—at least not immediately. They tilted their head and raised both hands, fingers forming smooth, practiced motions. "You're just trying to match me," they signed, brows lifting with playful accusation.

“PERHAPS,” Papyrus said, winking as though he'd kept up with every sign perfectly. He hadn’t. “BUT I’M DOING IT BETTER.”

Sans rolled his sockets. He was slouched back in the worn recliner they’d salvaged from a thrift shop two towns over—comfy in that way only decades of previous use could make a thing. One socked foot rested on the edge of the coffee table, his other leg crossed lazily over it. The flicker of the television danced across his cheekbones as his eyelights dimmed, boredom weighing down his sockets.

Metatton was on screen again—naturally. Humans couldn’t get enough of him. The metal glint, the spotlights, the perfectly timed sass—it translated well up here. Fame clung to him like perfume, and the talk show host currently gawking at his newest sapphire-studded jacket didn’t even try to hide it.

“he’s gonna need a crowbar to get that ego through the next studio door,” Sans muttered, dragging his thumb across his phone screen. “not that i blame 'im. guy knows how to milk a spotlight.”

A ping buzzed across his phone. He tapped it open and raised a bony brow. A message from Toriel.

'How is my child doing? she’d asked, warm and tidy as always. She still referred to Frisk that way—my child—even if Frisk now spent more time at the skeleton brothers’ place than the old schoolhouse.

“lookin’ like a lazy sunday,” Sans mumbled. He leaned forward, snapped a photo of Frisk and Papyrus sprawled out like overgrown cats, then added: 'relaxing. they’re safe. we’re all good, Tori.'

He hit send. Slumped back again.

There was comfort in the quiet. The kind of stillness that felt earned.

Outside, the sun dipped further past the windowpane. The light curled around the curtains in honey-yellow bars, brushing over cracked furniture and a stack of books Frisk had been nibbling through slowly. A mismatched mug rested on the floor near their elbow—forgotten tea going cold. On the wall, a calendar with a hand-drawn doodle of Napstablook hovered on today’s square, scribbled in with ’ambassador meeting - downtown hall’, and crossed out.

The TV flashed, static swelling for a second too long before Mettaton’s voice cut back in.

“OF COURSE, darling,” he purred onscreen, “I had to update my wardrobe for the new season. One must stay relevant, even if one was already perfect.”

Papyrus clapped. Frisk grinned without looking up. They began to sign something else, paused, and then spoke aloud instead, their voice soft and slightly gravelly from disuse. “He said that exact sentence last week.”

Sans chuckled. “copy-paste’s a hell of a drug.”

Papyrus tilted his head. “COPY… WHAT NOW?”

Sans opened his mouth to reply—probably with something punny and intentionally convoluted—when his phone buzzed again. He glanced down, screen lighting up with another message from Toriel. His sockets scanned the text, and a soft snort escaped him.

“heh. welp, mom says no adventuring tonight.”

Frisk turned toward him, one brow raised. They signed, "Why?", hands slow and questioning.

Sans shrugged, the corner of his mouth twitching upward. “weather’s takin’ a nosedive. guess the clouds don’t want us causin’ international incidents till the sun’s back out.”

Frisk groaned and flopped backward with a dramatic sigh, one arm over their eyes. “That’s boring…”

Papyrus, however, looked genuinely affronted. “WE’RE… JUST GOING TO SIT HERE? DOING NOTHING? LIKE YOU?”

Sans placed a hand on his chest, mock-wounded. “hey, pal. ‘s called energy conservation. very important. scientists recommend it.”

“THEY DO NOT.”

“do too.”

“NAME ONE.”

“me.”

Papyrus let out a long, withering groan that spiralled up toward the ceiling. “I AM SURROUNDED BY DEGENERATES WITH NO SENSE OF COMEDIC DIGNITY.” He stood up with a flare of his scarf, arms flailing dramatically as he turned toward the kitchen. “I SHALL FIND NO SANCTUARY HERE. PERHAPS IN THE FRIDGE I SHALL FIND SOMETHING TO CLEANSE MY SOUL OF YOUR... SKELE-TONIC HUMOUR.”

Frisk giggled, covering their mouth with one hand.

Sans leaned his head back against the cushion, watching his brother stomp off in a flurry of fabric and exaggerated despair. “he loves me, really,” he muttered.

Frisk climbed up onto the couch, legs tucking beneath them as they sat beside Sans. Their smile faded a little as their fingers moved again, slower now. "Sans..."

Sans turned his head, waiting.

"Do you think I'm... built for this? For being the ambassador?"

He blinked. The question didn’t surprise him, exactly, but it was rare that Frisk admitted this kind of thing out loud—even in sign. They usually kept their worries tucked away behind quick grins and stubborn optimism.

“hm.” He adjusted his position, one arm propped up on the couch armrest. “that why you’ve been extra fidgety lately?”

Frisk nodded, pulling their knees to their chest. “I’m trying,” they said aloud this time, voice quiet. “I really am. But what if I mess up? What if I say something wrong, or I miss something important, or I let everyone down?”

Sans considered them for a moment, all his usual deflective quips held back. Then he gave a small, lazy shrug. “then you fix it.”

Frisk looked at him, unconvinced.

“look, kid. i get it. folks see you like you’ve got all the answers. ‘cause you did a big thing, right? broke the barrier, saved the world, yadda yadda.” He waved a hand. “but none’a that means you gotta be perfect now. just means you gotta show up. even when it’s tough.”

They lowered their gaze, hands tightening around their knees. “But what if I can’t?”

Sans gently tapped their shoulder with the back of his phalange. “then you’ve got people. me. paps. tori. we got your back. you don’t have to carry all that weight alone, kiddo.”

Frisk bit their lip, then signed a soft “Thanks.”

Just then, heavy footsteps returned from the kitchen.

“WHAT IS THIS,” Papyrus announced in full capslock voice, “LOUNGING I SEE?”

He pointed a long, bony, gloved finger toward the couch like a knight calling out a heretic. “FRISK, HAVE YOU BEEN CORRUPTED BY THE HORRIBLE INFLUENCE OF MY BROTHER’S SLOTH?”

Frisk blinked, then grinned.

Sans held up his hands. “guilty as charged.”

Papyrus gasped in mock horror. “NOOO! NOT YOU TOO, HUMAN! YOU WERE THE CHOSEN ONE!”

Before Frisk could respond, Papyrus strode forward, swooped them up into his arms like a blanket burrito, and declared, “IF YOU’RE GOING TO BE LAZY, YOU’LL DO IT IN BED WHERE IT’S WARM AND ETHICALLY RESPONSIBLE.”

Frisk squealed in laughter, signing mid-lift, "Send help!" before their arms were too tangled in scarf and sleeves to continue.

Sans just snorted and leaned further into the cushions. “sorry, kid. bedtime means bedtime. skeleton law.”

“THIS IS NOT A REAL LAW,” Papyrus called over his shoulder as he carried Frisk toward the hallway.

“‘s in the bones,” Sans called back, pun lazy and well-worn.

Papyrus groaned like a wounded beast. “YOU’RE RUINING THE YOUTH.”

Frisk’s giggles echoed all the way to the spare room.

Sans sighed, finally alone in the warm flicker of the living room. He settled deeper into the couch, one arm behind his head, a small smile tugging at his mouth.

Outside, the wind began to pick up. The sky darkened in shades of blue and ink, pressing against the windowpanes.

Inside, everything was still.

For now.

Time passed.

Sans’s socketlights had long since dimmed, eyelids low and heavy, his skull tilted back into the couch cushion. Muffled TV static flickered somewhere in the background—Metaton’s dazzling voice had long faded into the white noise of late-night reruns. The soft sounds of the house at rest—the quiet creak of wooden beams, the distant tick of the kitchen clock, the faint hiss of the radiator—lulled him close to the edge of sleep.

The air outside the window was the deep velvet blue of pre-dawn, streetlights casting gold shadows across the floor. Just as he felt his consciousness give way to the sweet pull of sleep—

RING RING.

His phone shrieked to life, vibrating furiously against the coffee table. He jolted upright with a hiss, left eye flaring with startled blue light as his hand smacked at the device to silence it. His breath steadied when he saw Papyrus’s door still shut, the lights beneath it undisturbed. Frisk’s room was just as quiet.

“don’t worry,” he muttered to the house, “just your friendly neighborhood sleep-deprived skeleton. nothing to see here.”

He blinked down at the screen. ALPHYS.

“…this better not be about anime,” he groaned, rubbing the back of his skull as he accepted the call and dragged himself to the front porch.

The door creaked open gently, letting in the cold bite of early morning air. He leaned against the railing, bones folding in comfortably.

“yo, ‘phys. s’pretty late. or early. whichever. whatcha need?”

Her voice crackled on the line, high-pitched and apologetic, nervous even over the speaker.

“S-s-sorry, Sans, I—I know it’s super late, and I really wouldn’t have called unless I thought it was important, I swear! I just—there’s… something. A thing. I think it might be a big thing?”

Sans sighed, his eye flicking to the time. 1:43 AM.

“heh. you always save the good stuff for the graveyard shift.” He yawned wide enough his jaw cracked. “lemme guess—you in the new lab?”

“Y-yeah. Uh-huh. Uh—I mean, yes! The—y’know, the one in Ebott proper. With the safer floors and th-the better structural integrity and the snack drawer.”

“gotcha.”

And in a blink, he wasn’t on the porch anymore.

A familiar buzz filled the air, a static tug at space itself, and when the world blinked back into place, he was standing in the middle of Alphys’s cluttered new lab.

Alphys yelped and nearly dropped her tablet.

“SANS!! D-don’t do that!!” she flailed, clutching her chest. “You c-c-can’t just—!”

“break the fabric of spacetime? pretty sure i can. just did.”

She groaned, pushing her glasses up her snout. “One day you're gonna glitch yourself into a wall and I won’t feel bad at all.”

He grinned lazily, stuffing his hands into his hoodie. “nah. i’m too slippery.”

Alphys rolled her eyes, clearly too used to him to argue. “Okay, look. Over here.”

She turned and walked to the back of the lab, to a large wall-mounted screen surrounded by tangled wires and blinking servers. Sans followed, eyes narrowing.

The display was a constantly updating stream of data—spikes, dips, rhythmic pulses running in real time.

“what’s this?” he asked.

“Uh. So I, um… I still keep monitoring equipment rigged to the Underground. Y’know. In case anything, like, happens?”

Sans nodded slowly. “makes sense. someone’s gotta keep an eye on our old stomping grounds.”

“Right. So, everything’s usually… stable. Minor tremors here and there. The foundations down there aren’t totally inert, but it’s nothing wild.” She gestured with a claw to the leftmost side of the screen, where gentle, periodic pulses lined the graph. “See? That’s normal.”

She tapped the screen and scrolled sideways.

“But over the last three weeks… these started showing up.”

The screen scrolled toward a new section—taller, sharper spikes, scattered irregularly, some clustered, others isolated. The scale on the side ticked higher.

“that’s not… small,” Sans muttered.

“No. No it’s not,” Alphys said, mouth tightening. “At first I thought it was just sensor malfunction. But I re-ran the calibrations, replaced the hardware, checked from multiple points—Hotland, Waterfall, Ruins. They all show the same thing.”

She scrolled farther. The spikes rose higher. More frequent. More violent.

“Looks like a chain reaction building up,” she murmured. “At first, they were isolated. But now they’re converging.”

Sans stared at the jagged peaks. His fingers tapped against his hoodie pocket, slow and thoughtful.

“…looks like the beginnings of an earthquake,” he finished.

Alphys nodded grimly. “Exactly.”

A long silence passed between them.

The fluorescent light flickered slightly overhead, humming against the quiet.

Sans rocked on his feet. “you sure it's natural?”

“I—I don’t know.” Her voice lowered. “That’s what I wanted your input on. Because the thing is… some of the readings? They’re coming from areas that shouldn’t be active. Like, sealed zones. Places no one goes. Not even the CORE’s ruins.”

“...you think it’s something waking up?”

She looked at him, eyes wide. “I don’t know. But it’s getting stronger.”

Sans exhaled slowly. He looked back to the screen, watching the tremors continue to spike.

“so… what’s the plan?” His voice was low, quiet, the glow in his left socket dimming as his fingers rested against the console’s edge.

Alphys tapped a few keys, pulling up a wider feed of the seismic logs. “I—I wanna go down there. T-To get a proper look. The data’s only part of it. I need to see what’s causing this firsthand.”

Sans tilted his skull. “you sure that’s a good idea, al? place hasn’t exactly aged like fine wine.”

She nodded, though her posture was tight. “I won’t go alone. U-Undyne’s coming with me. She… she insisted, actually. Said, uh, ‘I’m not letting you go into some suspicious underground meltdown zone without a battle buddy,’ or—y-you know, something like that.”

Sans smirked, crossing his arms loosely. “sounds about right. you two been spending a lotta time together, huh?” He cocked a brow ridge. “this a date disguised as disaster response?”

Alphys flushed a deeper yellow, eyes widening. “Wha—! N-No! Sans!” She tugged at her lab coat sleeve and turned back to the monitor. “Ugh, you’re the worst.”

“guilty as charged,” he drawled, though there was something heavier under his tone—something that lingered in the space between jokes and tremors.

Alphys cleared her throat, half-sputtered through the next sentence. “I… also wanted to ask if you’d come with us. Y-You know your way around this kinda stuff. You’re—uh—you’ve always been good at, uh, anomalies.”

Sans arched a brow. “anomalies, huh? you makin’ that a compliment or a diagnosis?”

“I-I mean it! You helped me run simulations for years. You’re calm under pressure. A-And you’ve got a better eye than anyone for when something’s... off.”

He stared at her a moment, then let out a slow sigh. “yeah, alright. guess i could use a walk down memory lane. stretch the ol’ phalanges.”

Alphys smiled, a mixture of relief and nerves. “Papyrus can come too, if—if he wants. I mean, it might be good to have him around. You know how… thorough he is.”

Sans laughed, low and fond. “he’s not ready. you’re not ready. ain’t nobody ready to see the great papyrus and undyne team up again. they’ll have half the underground triple-scrubbed by noon.”

“I’m emotionally bracing myself already,” Alphys muttered, adjusting her glasses.

Sans stepped closer to the screen, sockets narrowing. “what exactly you think’s causing this, al? you got a guess?”

She hesitated. Her claws hovered over the keyboard, then dropped. “I… don’t know. Honestly, that’s what’s freaking me out. The CORE’s dormant. Power draw’s low. And all the major facilities are supposed to be empty.”

“but?” he asked.

She pointed to the largest spike in the log, a tremor that had broken through the baseline like a jagged knife. “But someone—or something—is moving down there. And they’re getting bolder.”

He was quiet for a moment. Just the whirring hum of the monitors filled the air.

“how long you been planning this?”

Alphys turned to look at him, her expression unusually serious. “Since the first major spike. About… six weeks ago. I wanted to make sure it wasn’t just residual stress. But the pattern's too consistent now. Something’s changed.”

Sans rubbed at his neck, the vertebrae clicking slightly as he rolled his shoulders. “alright. i’ll talk to pap tomorrow. maybe frisk, too. they might wanna tag along.”

Alphys gave him a wary look. “Are you sure? I mean—they’re the ambassador. If anything goes wrong—”

“they’ll be fine,” Sans interrupted gently. “kid’s tougher than they look. and besides… they’ve got a right to know if something’s wrong underground. it’s still part of their job, isn’t it?”

Alphys nodded slowly. “Yeah… Yeah, I guess you’re right.”

The screen blinked again. Another tremor. This one smaller, but unsettling in its rhythm—like footsteps.

Sans frowned. “might wanna pack more than clipboards, al. something tells me this trip’s gonna be more than a science field day.”

She swallowed hard, then turned to begin shutting down the system for the night. “I’ll make a checklist. G-Goodnight, Sans.”

“night, al.” He vanished with a soft blink of blue light.

Back on the porch, the air was colder now. The stars were out, and the city was quiet—just the distant hum of traffic and the faint glow of lights in windows. Sans tucked his phone back into his hoodie pocket and gazed up at the sky for a moment.

Somewhere below all this, the Underground was stirring again.

He didn’t like it. Not one bit.

He checks on his brother, feeling a little guilty that he missed telling Papyrus’ bedtime story—but the feeling softens into something fond when he catches sight of Frisk, curled up between the pillows, the well-worn Fluffy Bunny’s Big Adventure book clutched loosely in their hands. Their hair was a wild halo against the pillowcase, one sock half-off, the other foot poking out from the blanket.

Sans smirks.

“typical,” he murmurs under his breath.

With practiced care, he reaches out and slides the book from Frisk’s fingers. They stir, but don’t wake. One of their hands shifts, forming a familiar sign without thought: safe.

He stares at it for a second, then tugs the red-and-orange blanket up over them. It’s the one Toriel crocheted last winter, the one his brother refuses to sleep without. His phalanges hover for a moment before gently tucking the blanket in around their shoulders, casting a glance at the other side of the bed where Papyrus snores.

Papyrus mumbles something in his sleep. Something about puzzles. And spaghetti.

Sans backs out of the room, each step slow and silent. At the door, he mumbles a soft, “night, boneheads,” before shutting it with the quietest click.

His room is next door. The door creaks as he opens it—Papyrus keeps saying he should oil the hinges, but Sans says the noise helps him know when someone’s trying to sneak up. Of course, no one sneaks up anymore. Not up here.

Not on the surface.

The room is… tidy. Painfully tidy. The walls are bare except for a single framed picture of the solar system, Papyrus insisted they hang to “elevate the space.” The desk is spotless. The bed is made. Too made. Crisp corners. Smoothed sheets.

Papyrus had demanded it stay that way.

“The surface is a new beginning, Sans! We can’t sully it with your… chronic horizontalness!”

So Sans had agreed. In his own way.

He sleeps on top of the covers, hoodie and all. If he never gets under them, he never messes them up. Problem solved.

He flops down now, limbs sprawled, staring up at the ceiling. The plaster’s too smooth. Too white. No cracks. No shapes to make out in the lines like in their old house. He folds his arms beneath his skull.

The lamp clicks off with a flick of his magic. Darkness settles.

For a while, he just listens—to the faint hum of the fridge, the muted tick of the hallway clock, the gentle thud of a radiator kicking on. It’s quiet. The kind of quiet that should be comforting.

It is. Mostly.

Things have been better. Really better. Frisk had adjusted to life topside like they’d always belonged there. Papyrus had taken to it like a sponge to water. Even Alphys and Undyne were doing alright—more than alright. Monsters had homes. Jobs. Lives.

And him?

Well, he hadn’t woken up with a timeline splintering around him in a long while. That counted for something.

Frisk had promised they’d never reset. Not again. Not ever.

He believed them.

He did.

He—

His sockets blink.

A flash. White-grey dust. A red scarf. Wind howling through cracked pine. A crunch underfoot. A whisper of a name—

No.

No. He shuts his sockets, jaw tightening.

He wasn’t thinking about that.

Wasn’t thinking about the last time someone said never. Wasn’t thinking about promises. About consequences. About how fragile the world had felt the first time he held it in his hands and had to watch it die.

His face pinches. He rolls onto his side and tugs his hood over his skull like a blanket.

He’s not back there. Not in Snowdin. Not in the cold. Not in the dust.

He’s on the surface.

The mattress creaks beneath him as he breathes out slow.

Tomorrow, he’ll wake up to birdsong and burnt toast. Papyrus will be yelling about calcium intake. Frisk will be half-asleep, signing something sarcastic without even opening their eyes. Alphys’ll probably text him a new batch of tremor readings.

And he’ll be here. Just like he said he’d be.

He has to be.

He drifts off eventually, not into dreams, but into something quieter. Something still.

Something that—for now—feels like peace.

Chapter Text

The trio stood outside Toriel and Frisk’s home, a warm breeze tugging gently at Papyrus’ scarf as flower petals swirled through the air. The house itself was small but inviting—cream-coloured bricks partially hidden behind ivy, tall windows framing soft golden light, and a small wooden fence painted pale blue, with a gate that squeaked ever so slightly when opened. The garden was as lovingly tended as ever, bursting with vibrant, fragrant life. Neatly trimmed hedges ran along the edges, and clusters of golden flowers swayed lazily in the wind.

It was Papyrus who first noticed the familiar pair of horns amidst the tall sunflowers.

“IS THAT… THE FORMER KING HIMSELF?” he gasped, pointing dramatically with a white-gloved hand.

Asgore stood among the flowerbeds, a straw hat perched awkwardly atop his head, holding a watering can far too small for his bulk. The former king looked up, blinking slowly before giving a sheepish smile and a small wave.

Frisk waved back immediately, grinning with a spark of excitement in their eyes. Their fingers fluttered up in a quick sign: They’re talking again!

Sans tilted his head, amused. “heh… thought that was a myth.”

Frisk nodded quickly, switching fluidly to speech. “Mom said it was gonna happen eventually. I just... didn’t think I’d actually see it.”

“THEY APPEAR TO BE WORKING TOGETHER IN HARMONY,” Papyrus added, beaming. “HOW SPLENDID! PERHAPS THEY SHALL ONCE AGAIN HOST ROYAL TEAS.”

“only if they survive the awkward small talk,” Sans muttered under his breath, shoving his hands deeper into his hoodie pockets.

Asgore noticed the trio approaching and straightened, brushing a bit of dirt off his apron. “Ah! Good morning, my friends. It’s lovely to see you all. Frisk, Toriel’s inside—she’s been baking all morning.”

Frisk signed a quick thank-you and bounded past the gate, practically vibrating with excitement at the promise of cinnamon butterscotch.

Papyrus followed behind, waving animatedly at Asgore, who gave a soft chuckle in return. Sans lingered a little longer, his eye sockets narrowing slightly—not in suspicion, just in thought.

“y’know,” he muttered as he passed Asgore, “coulda picked a better time to grow a green thumb, bud.”

The goat monster didn’t respond right away, just watched the skeleton go with a wistful sort of smile, then turned back to his flowers.

Inside, the smell of warm sugar and butter hit them instantly. Frisk inhaled deeply, kicking off their shoes and padding into the kitchen where Toriel stood at the counter, pressing the edge of a pie crust into a dish with expert precision.

She looked up, eyes softening immediately. “Ah, my child! Sans. Papyrus. You’re just in time—tea is ready.”

Papyrus placed a hand over his chest dramatically. “LADY TORIEL, YOUR HOSPITALITY CONTINUES TO AMAZE!”

“thank goat,” Sans said, flopping into a chair with a groan. “long walk. tired bones.”

Frisk laughed softly, perching beside him on the bench and leaning against his shoulder for a moment before sitting up straight again. They reached for the teapot and began pouring cups with practiced grace, careful not to spill.

Toriel smiled at the scene, wiping her hands on her apron before taking a seat herself. “I imagine you three didn’t come all the way here just for tea,” she said gently, eyes flicking between the trio with knowing warmth.

Frisk glanced at Sans, who shrugged as if to say, you wanna explain, or should I?

Frisk lifted their hands, hesitant, then began to sign slowly. We think something’s wrong in the Underground. Alphys saw—

They stopped, frowning slightly, then switched to speech. “—she saw readings. Spikes. Earth tremors. She’s worried. We’re gonna go check.”

Toriel’s brow furrowed, but she didn’t look surprised. “I had heard… rumblings. I hoped it was simply natural settling. The Earth adjusting.”

“could be,” Sans said, “but it’s a bit more than your standard tectonic tantrum. alph wants to check the labs. maybe the core.”

Toriel placed her cup down gently. “The CORE…” she murmured, concern deepening. “That place holds so many... unpredictable variables.”

Papyrus puffed up. “WHICH IS WHY WE SHALL VENTURE FORTH AND INVESTIGATE! RIGHT, FRISK?”

Frisk gave a small smile, nodding, but it was tight at the edges. Their fingers twitched in their lap before they signed again: Just checking. That’s all.

Her voice was soft, warm—measured with the kind of wisdom that only came from pain endured and endured again. She leaned down, brushing a tender kiss to Frisk’s forehead. The gesture was quiet but grounding, reverent in its simplicity. The child nodded once, holding her gaze for a heartbeat before stepping back.

Toriel's hands moved with practiced ease as she adjusted the straps of their backpack, tugging the worn fabric into place with motherly precision. She smoothed a crease at Frisk’s shoulder, then stepped back, her fingers clasping in front of her apron as the child moved to stand between the brothers.

“Please,” she said gently, looking from one skeleton to the other. “Watch over them.”

“WORRY NOT, FOR I, THE GREAT PAPYRUS, SHALL GUARD THEM WITH MY LIFE!” Papyrus’ voice was as radiant as the early sun peeking over the hilltops, brimming with his usual gallant energy. He saluted her with a sweeping gesture, nearly hitting Sans in the skull.

“heh,” Sans chuckled, unfazed as always. “don’t worry, tori—we’ll bone up on our babysitting skills.”

Toriel chuckled warmly, shaking her head, the tips of her ears twitching fondly. “You haven’t changed.”

“nah. just better lighting up here,” he said with a wink, and her laughter followed them as she reached for the doorknob again.

“If you need a lift—”

“nah, we’re takin’ a shortcut,” Sans interrupted casually, already raising one hand. His fingers curled gently over Frisk’s shoulder, the other hand clapping against Papyrus’ back.

“see ya, tori.”

And with a blink—
—they were gone.

The bright sun was replaced in a blink by overcast grey and the biting wind that always curled at the base of Mount Ebott. Clouds loomed thick above the treeline. The scent of distant moss and wet rock filled the air. Mist clung to the ground in low sheets, twining through the gnarled trees and scattering pale light like thin smoke.

Frisk huddled closer to Sans as they emerged, their boots crunching faintly on gravel. A few leaves danced around their ankles, carried by the breeze.

Ahead, a familiar figure paced near the mouth of the path—tall, powerful, and immediately recognisable even in the haze.

“Yo!” Undyne called out, raising one hand over her head. Her eyepatch was slightly askew, and her stance suggested she’d been waiting a little too long.

Papyrus blinked rapidly, swaying slightly on his feet as the teleport left his balance a step behind. “I DESPISE THAT YOU HAVE A POWER THAT ENABLES YOU TO BE EVEN LAZIER THAN YOU ALREADY ARE, SANS!”

“hey, it’s efficient,” Sans replied with a lazy shrug. “i call it... fast travel.”

Papyrus groaned and began his dramatic march forward, striking a sharp salute toward the waiting warrior. “UN-DYYYYYNE! THE GREAT PAPYRUS REPORTING FOR DUTY!”

Frisk snorted through their nose and signed quickly with one hand, their other still adjusting the strap on their bag.

He really does take this stuff seriously, huh?

Sans only chuckled, watching as his brother practically leapt into Undyne’s waiting presence like a soldier eager for a new mission. The mist curled behind them, wrapping the path in quiet, broken only by the sound of distant birds and the steady pulse of wind weaving through the pines.

He turned to Frisk and gave them a small nudge. “you ready, kid?”

Frisk nodded, their expression steadier now, though they still signed slowly.

I think so. Just don’t let Papyrus talk Undyne into yelling the whole time.

“no promises,” he replied with a lazy grin.

Behind them, the silhouette of the house was already swallowed by fog. Ahead, the trail curved down into the trees—quiet, steady, unknown.

Sans and Frisk slowly caught up, their footsteps muted by the earth beneath them. The path curved gently into the clearing ahead, and that’s when they spotted her—Alphys—leaning half-hidden behind the open back of the couple’s weathered pickup truck, clipboard tucked beneath one arm and her tail twitching nervously against the bumper.

The lizard-like scientist startled when Sans stepped into view, his trademark slouch unmistakable even in the mist.

"yo," he said simply, hands in his pockets as always.

Alphys let out a sharp yelp and nearly launched the clipboard into the bed of the truck. “G-gah! Sans! Frisk! You guys are—oh, wow—you’re earlier than I thought.”

Frisk offered a small wave, their other hand moving to rest against the edge of Sans’ jacket. They signed a single word with a faint smile: 'Hi.'

Alphys pushed her glasses up her snout and exhaled sharply. Her nerves hadn’t dulled much, even since the surface settled into a quieter pace. “H-hi! Uh—okay, okay, s-so the plan—right!”

She flipped through a few scribbled notes, muttering to herself for a second before remembering they were still standing there. “R-right. We’re gonna head down to my old lab in Hotland. I wanna assess the damage from the tremors firsthand—make sure nothing’s leaking or unstable. I mean—some of that equipment is super delicate, and if it’s compromised, there could be... uh, issues.”

“science-y issues?” Sans quipped, one browbone raised.

Alphys nodded, eyes wide behind her cracked lenses. “Y-yeah. Like, super serious ones.”

There was a sudden bark of laughter from the other side of the truck.

"WE’RE GONNA DO COOL SCIENCE SHI—" Undyne, halfway through hoisting Papyrus into a dramatic headlock, abruptly caught herself midword. Her one eye darted toward Frisk, who was blinking up at her.

“—Stuff,” she corrected quickly, clearing her throat and trying to play it cool. “Cool science stuff.”

Papyrus, still flailing in her grip with flustered indignation, wheezed. “UNDYNE! I DO NOT BELIEVE WRESTLING COUNTS AS A SCIENTIFIC METHOD!”

“You’d be surprised what you can learn in a full nelson,” Undyne said smugly, tightening her hold a bit before finally letting him go. Papyrus tumbled dramatically into the truck's tailgate with a clatter of bones and pride.

Frisk stifled a laugh, covering their mouth with the sleeve of their hoodie, and Sans grinned sideways, glancing toward Alphys again.

“so—just the lab? or is this a grand tour of the underground’s finest ruins?”

“W-well... mostly just the lab,” Alphys said, her voice still shaking slightly. “But I’d like to check the entrance to the CORE too. I-it’s been sealed since the evacuation, but if these spikes are messing with structural integrity, the magic conduits might—uh—destabilise. And that would be... bad. Really bad.”

“bad enough to justify a field trip?” Sans asked, voice light but not unkind.

Alphys hesitated. Then nodded once, firmly this time.

“Yes,” she said. “I’ve been keeping an eye on the readings since the first major spike. That was... about three weeks ago now. I thought maybe it was just ambient decay from unused infrastructure. But they’re getting stronger.”

Frisk's hand stilled against Sans’ coat. They looked up at him, something quiet in their expression. When they spoke, it was soft.

"Will it hurt people?"

Alphys’ ears drooped. “That’s what I’m trying to prevent.”

Sans sighed and rubbed the back of his neck, eyes flicking toward the mist curling around the base of the mountain. “alright. guess that’s enough science stuff to warrant tagging along.”

“AND I SHALL ACCOMPANY YOU FOR THE SAKE OF SAFETY AND NOBILITY AND POSSIBLY SNACKS!” Papyrus declared, now dusting himself off as if he hadn’t just been turned into a pretzel by Undyne. “THE GREAT PAPYRUS NEVER ABANDONS HIS FRIENDS IN TIMES OF MINOR TO MODERATE SCIENTIFIC DANGER!”

“You hear that, Alphys?” Undyne elbowed the smaller monster gently. “We’ve got backup. The tallest backup.”

Alphys gave a shy little smile, her tail curling around her ankle as she glanced between them. “Thanks, guys. Really. I wasn’t sure if you’d want to come, but... it means a lot.”

Sans shrugged, the movement lazy as ever, but his eye sockets were more focused than usual. “gotta make sure nobody ends up in another explosion. or... worse.”

There was a beat of quiet.

Frisk signed slowly. 'We won’t let that happen.'

“Darn right, squirt,” Undyne said, reaching over to gently ruffle their hair before turning to start loading a few supplies into the truck’s bed. “C’mon, everybody! Saddle up!”

Papyrus gasped. “I CALL SHOTGUN!”

“Nope,” Undyne barked, pointing a thumb over her shoulder. “That’s for the person who can navigate and not distract the driver by reciting spaghetti ingredients.”

“THAT IS A GROSS MISINTERPRETATION OF EVENTS, UNDYNE!”

Sans chuckled as the pair bickered their way to the cab. Frisk lingered by the truck bed, watching Alphys tie down a crate of equipment with silent precision.

The child spoke again, voice low. “You scared?”

Alphys looked up, blinking. “W-what?”

Frisk repeated the question in sign, slower this time. 'Are you scared?'

Alphys was quiet for a long moment. Then, in a whisper, “Yes.”

Frisk nodded, resting a hand briefly on the crate between them. “Me too.”

Sans watched the exchange from a few paces away, something unreadable flickering behind his grin.

He didn’t say anything.

The ride up to the entrance wasn’t awful, all things considered.

The truck jostled and growled beneath them as it wound its way along the dusty old service road that curled through the overgrown woods like a snake too lazy to slither straight. The dirt track was sunbaked and pitted, riddled with potholes and flaking bits of gravel, but the vehicle powered through it with a kind of relentless enthusiasm that could only come from Undyne’s lead foot on the gas pedal.

In the cab, Sans had let his eyes slip shut, body loose and still. He leaned against the inner wall with his arms crossed, the faintest smirk tugging at his jaw. Not quite asleep—but close. He didn’t need to open his sockets to appreciate the scene.

Undyne was hollering about the dust.

“THIS ROAD IS A CRIME SCENE! WHO ALLOWED THE SURFACE TO HAVE THIS MUCH DIRT?!” she bellowed, one arm flung across the wheel while the other waved dramatically out the open window. “MY TRUCK WAS CLEAN THIS MORNING, ALPHYS! CLEAN!”

“I-I don’t think it counts as dirty if it’s just—d-dust,” Alphys squeaked from the passenger seat, both her claws currently shielding her eyes as though it might protect her from the rough, bouncing blur outside the windshield. “Oh god. That was a pothole. Undyne, are you sure this thing has brakes?!”

“DON’T WORRY! I INSTALLED THEM MYSELF!” Undyne shouted with a grin, flooring the accelerator.

“That doesn’t make me feel better!”

Behind them, in the open truck bed, Papyrus was clinging to Frisk like a lifeline. The tall skeleton’s long legs were braced against one side of the bed, while his arms wrapped protectively around the child’s middle, keeping them from being flung into orbit every time the truck hit a sharp turn. His skull clattered faintly with each jolt, and his entire frame rattled like a xylophone in a thunderstorm.

“THIS IS DEFINITELY—AND WITHOUT QUESTION—THE MOST PERILOUS MODE OF TRANSPORTATION I HAVE EVER EXPERIENCED!” he cried, voice carried off by the wind. “FRISK! IF I DO NOT SURVIVE THIS RIDE, REMEMBER ME AS I WAS—DIGNIFIED AND STRONG!”

Frisk, wedged snugly into his side like a determined barnacle, was laughing. Their hair whipped wildly around their face, and the air stung their cheeks, but their smile was bright and unafraid. The danger was performative, the kind born of mischief and poor decision-making rather than true threat. Their hands moved swiftly in front of them, trying to keep steady.

'You’re gonna be fine.'

“IF I AM NOT, I WOULD LIKE A HEROIC BURIAL, COMPLETE WITH A PARADE!”

Frisk chuckled again and reached up to pat his ribs, eyes crinkling with amusement.

Inside the cab, Alphys had begun talking again, voice rising slightly over the roar of the wind.

“I-I just think we should all be cautious, okay?! There could be pressure fractures, or unstable tunnels, or—o-or lingering magical contamination in the CORE wiring. If any of the thermal regulators in the deeper chamber cracked, the geothermal conduits could flood the lower deck in seconds. Not to mention the chance of latent magic—!”

“NERD ALERT,” Undyne yelled cheerfully.

Alphys chuckled. “I say y-you stay back and let me and Sans the Secret Science Guy go handle the b-boring explosions.”

Undyne frowned. “Sans isn’t even—wait, Sans? Since when are you a science guy?!”

Sans opened one eye. “since... i decided it was cool.”

Undyne barked a laugh. “Pffft! Since when do you do anything that isn’t 90% naps and bad puns?”

“hey, i’m highly specialised,” Sans said lazily, tipping his head toward her. “i study theoretical... bone structure. it’s very... skeletal.”

There was a pause.

Then Undyne groaned, full-body and guttural. “NOPE. Nope nope nope. That’s it. I swear to Asgore I will turn this car around right now.”

“do it,” Sans said. “i dare you. i’ve got five more puns locked and loaded.”

Alphys let out a tiny whimper and leaned harder into her hands.

“Why did I agree to this.”

“You needed backup,” Undyne said with a wink. “Now you’ve got muscle, bones, and a brain - Frisk's. We’re unstoppable!”

Outside, the trees grew thicker. Moss clung to broken stone markers long since overtaken by nature. The path narrowed to a canyon of green and shadow. The deeper they drove, the more the light filtered through the leaves in strange, fractured rays—like the world had fractured alongside the mountain. The air took on a coppery tang, faint and flickering at first, then unmistakable.

Papyrus sniffed dramatically as the truck bumped over a root.

“I SMELL... SCIENCE!”

Frisk laughed again, brushing hair from their face and glancing toward the trees. The entrance to the underground was close now—they could feel it. There was a strange kind of pressure in the air, a faint thrum that echoed somewhere in their bones. Not a sound. More like the memory of a sound. Something ancient. Something waiting.

Sans felt it too.

He sat up slightly in the cab, one hand resting on the back of Alphys’ seat. His grin had faded to something more thoughtful. Not quite frowning, but far from amused.

“hey, al,” he said softly.

She glanced back at him.

“...you said the spikes started three weeks ago?”

“Y-yeah.” She swallowed. “Why?”

Sans didn’t answer right away.

Instead, his eye sockets narrowed. He looked out the windshield toward the winding road ahead, where the trees began to thin and the dark mouth of the entrance loomed like an old scar on the hillside.

“just makin’ sure my calendar’s not off.”

Alphys turned fully in her seat, brows furrowing. “Sans, what are you talking about?”

But Sans didn’t answer. He just leaned back in his seat and closed his eyes again.

Undyne frowned but didn’t press him. The wind whipped through her hair, and the wheels rolled on.

They made it to the entrance.

The truck's engine grumbled into stillness, the tired creak of its frame settling into the silence that followed. The thick trees overhead filtered the sunlight into ribbons, casting jagged shadows across the old, moss-coated stone path that wound down toward the chasm of Hotland’s outskirts.

Doors slammed.

Sans rounded the back of the truck just as Papyrus lurched out of the bed with all the poise of a wet noodle. The taller skeleton hit the ground in a stumbling heap, limbs flailing as he caught his balance and struck a shaky pose of triumph.

“NYEH—!” he blurted, voice pitching wildly as he straightened. “THAT WAS THE BEST RIDE EVER!”

His eye sockets sparkled with genuine exhilaration, and though his bones wobbled slightly under him, he struck a victory pose with arms raised high like a champion gymnast who’d just landed a flawless routine—despite, in this case, having been flung around like a ragdoll in a glorified tin can.

Undyne barked out a laugh, tossing her keys from hand to hand before catching them behind her back.

“THAT’S WHAT I’M TALKIN’ ABOUT! A REAL HERO’S RIDE!” She gave Papyrus a solid slap on the back, which sent his torso lurching forward and nearly knocked his skull off. “You survived the UNDYNE EXPRESS! Five stars, no seatbelts, and absolutely no regrets!”

“IT WAS VERY DANGEROUS AND I LOVED EVERY SECOND!” Papyrus beamed, straightening with pride.

Frisk hopped out next, landing softly beside him. They gave the truck a skeptical glance and raised their hands to sign.

'Pretty sure I bounced off the floor at one point.'

Papyrus gasped, placing a hand over his nonexistent heart. “FRISK! IF YOU WERE INJURED, I WOULD HAVE LEAPT TO YOUR DEFENSE IMMEDIATELY. EVEN IF I HAD TO SACRIFICE MYSELF TO THE TRUCK GODS!”

Frisk giggled and patted his hand.

'It was fun. Just saying.'

Sans let the scene wash over him with a quiet sort of fondness, his grin small but genuine. The dust from the drive still hung in the air, catching the filtered light and giving everything a hazy, nostalgic edge. He took a slow step toward Alphys, who stood a little ways off from the others, hunched over her tablet.

She hadn't moved since exiting the vehicle.

Her claw tapped through holographic screens, data scrolling faster than even Sans could fully track. Energy readings. Pressure fluctuations. Heat maps, by the look of it. Her mouth moved in a silent count, lower lip caught between her teeth.

“yo,” Sans greeted, coming to a stop beside her.

She startled slightly, nearly dropping the tablet. “O-oh! S-sorry—I didn’t hear you.”

“yeah, wasn’t really shoutin’. everything good?”

Alphys hesitated. Her gaze flicked back to the screen. “M-mostly. The data’s still incomplete, but... some of the readings look worse than I expected.”

He tilted his skull, casual but attentive.

“worse how?”

She exhaled through her nose. “The deeper geothermal layers under the CORE—they’re spiking hard. Like, real hard. The containment field hasn’t breached yet, but if these trends keep going...” She trailed off and made a helpless motion with her hand. “We’ll need to do a full diagnostic from my lab. These readings are too patchy to trust.”

Sans nodded slowly, the lines of his face settling into something more serious.

“so, shortcut it is?”

Alphys hesitated again. Her fingers froze above the display.

“I... I don’t think we should,” she said finally. “Teleportation magic draws from ambient energy. If the CORE’s systems are already unstable, skipping space could feed back into the—well, the wrong circuits. Worst-case scenario, you land inside something.”

“...like a wall.”

“Or a reactor coil.”

Sans winced. “yikes.”

“Exactly. I—I know it’d be faster, but... I’d rather we take the long way down.”

“hey, works for me.” He offered a lazy shrug. “never hurts to stretch the legs.”

They shared a small, quiet look. Then, with a nod, Sans turned to follow the others.

Ahead of them, Undyne had already begun leading the way down the path, her boots thudding against cracked stone in a confident rhythm. Her spear was slung casually over one shoulder, and every step she took kicked up a puff of dust. Papyrus marched dutifully beside her, legs long and precise, narrating their descent like a tour guide with a flair for the dramatic.

“AND HERE WE HAVE THE HISTORIC ENTRANCE, A MARVEL OF ARCHITECTURAL—”

“Paps,” Undyne cut in, “it’s a cave. You don’t gotta narrate.”

“BUT THE PEOPLE MUST BE EDUCATED!”

Frisk trailed just behind them, their eyes wide as they scanned the jagged edges of the descending trail. The path narrowed quickly—old, half-buried rail lines split and twisted through the rock, long since rusted over. Vines clung to broken columns, and deep fissures spiderwebbed through the stone. The earth felt tired. Like a creature disturbed from its sleep.

Sans stepped up beside them, his gait relaxed as ever. He kept one socket on the trail, the other on the kid.

“you good?” he asked quietly.

Frisk nodded.

Then they signed.

'Something feels... weird.'

Sans didn’t respond right away. Just kept walking, hands in his pockets. The heat in the air was faint but rising. The closer they got to the true edge of Hotland, the more the stone seemed to hum. That low frequency again—the kind that prickled in the back of your mind but never quite reached your ears.

“yeah,” he said at last. “me too.”

They kept going.

They began their descent through the older passages of the Underground, past roots that cracked through ceilings like crooked fingers and walls stained with the minerals of a thousand years of solitude. The deeper they went, the more the air thickened—warm, heavy, and laced with the quiet sigh of unseen steam vents breathing slowly through stone.

Judgment Hall stood silent as they passed. Its towering, somber columns framed the entry like a ribcage, and the gold glow of the old chandeliers flickered with a ghostly dimness, powered now only by residual energy. The silence was different here—not just quiet, but expectant, like the place remembered what had happened within it.

Undyne slowed, her boots scuffing against the marble floor.

“You know,” she muttered, glancing up at the ceiling’s faded murals, “I never got to meet the royal judge. Not once.”

Papyrus straightened beside her. “THE LEGENDARY ‘JUDGE’ OF THE UNDERGROUND! THE SHROUDED SHADOW OF JUSTICE! THE MYSTERIOUS FIGURE OF FINAL FATES!”

Undyne snorted. “Yeah, that guy.”

“OR GIRL,” Papyrus added quickly, one finger raised. “THEY NEVER REALLY SAID. BUT WHOEVER IT WAS, I GOTTA BE HONEST… THEY GAVE ME THE HEEBY-GEEBIES.”

He shivered dramatically, bones clattering with exaggerated flair.

Frisk, walking just a few steps ahead, slowed and glanced sidelong at Sans.

They raised a single brow, an expression they'd perfected during long afternoons of learning how to read sarcasm in a land of talking flowers and time loops.

Sans caught their look, his grin going just a bit sharper. He pressed one finger to the side of his mouth in a mock shhh gesture, sockets squinting with playful secrecy.

Frisk rolled their eyes but smirked. Their fingers flicked subtly in response as they resumed walking.

'Suspicious.'

The hallway faded behind them.

The architecture began to shift as they neared Newer Home—the once-pristine corridors losing their polish to creeping vines and collapsed archways. Debris littered the edges of the path like forgotten offerings, and the light from the far-off ceiling had grown soft and dappled, filtered through layers of damage. A fine sheet of dust coated everything, like the whole world had paused to sleep and hadn’t yet bothered to wake.

Undyne sniffed.

“Ugh. Place looks like it’s been through a hurricane.”

Frisk paused to rub a finger through the dust on a wall. It came away dark and smudged, the pattern left behind revealing a faint glyph once carved proudly into the stone.

Alphys stepped around them, rubbing her arm. “Actually, now that the barrier’s gone… the Underground’s experiencing natural airflow again. Weather systems are finally reaching this deep.”

Papyrus gasped. “YOU MEAN… THIS IS… OUTSIDE WEATHER?!”

“Sort of,” Alphys said with a faint shrug. “The currents are weak and indirect, but wind, moisture, and even small temperature shifts have started trickling down here. It’s making things look more worn, but technically, that means life’s finally moving.”

Undyne made a face. “Great. So it’s not neglect, it’s progress. Dusty, gross progress.”

“IT IS STRANGELY POETIC,” Papyrus declared, stepping carefully over a loose brick. “LIKE TIME ITSELF IS LEAVING FINGERPRINTS ON OUR HOMES.”

“yeah,” Sans muttered from the back of the group, voice low. “or footprints.”

The others didn’t hear him. They were already moving on, Undyne animatedly reenacting a moment from Frisk’s fight with Flowey, her arms sweeping wide in overblown motion as she twisted her face into exaggerated horror.

“—AND THEN YOU WERE LIKE SHWOOM, RIGHT THROUGH THE VINES, AND THAT FLOWER DUDE WAS ALL NYEHHHGH!” she demonstrated with both arms flailing in imitation of a wilting plant. “AND THEN BAM! LIGHT BEAMS! EVERYONE’S ALIVE! IT WAS WILD.”

Frisk laughed, their shoulders shaking as they signed clumsily between steps.

'You made me sound way cooler than I was.'

“NO WAY,” Undyne grinned, clapping them on the back. “YOU TOTALLY NAILED IT. WE WERE ALL THERE—WELL, I WAS KINDA STUCK IN A POD—BUT THE POINT STANDS.”

Sans stayed several paces behind, the click of his slippers softer than the others’ heavier steps. His eyes lingered not on the people but the walls. The floor. The shadows between cracked pillars.

Everything had changed.

But it hadn’t.

The place looked worse for wear, sure. But the shapes, the turns, the scuffed grooves left in stone from a decade of repeating footsteps—they were the same. Like the Underground had been caught between decay and memory. Like it wanted to forget, but couldn’t quite let go.

He remembered the sound of the Judgment Hall, how quiet it got when someone reached the end. How the air would hum in that impossible way, a resonance only he could hear.

He remembered waiting.

He remembered speaking.

He remembered deciding.

There was no real weight in his steps as he moved, no hurry, no sound. Just presence.

His thoughts drifted loosely as the others chatted ahead—recollections folding in on themselves like paper in water. The way Frisk had held the timeline together. The way Flowey had snapped it. The look in Papyrus’ eyes when they’d first surfaced. How quiet Grillby’s had been on the last day.

His sockets half-lidded. A faint breeze rustled through the ruined ceiling above, stirring the dust like breath on glass.

He didn’t look up.

He already knew the sky wasn’t there.

As time passed, their steps fell into rhythm, slow but steady against the uneven stone beneath them. The corridor arched wider ahead, the walls slick with mineral gloss and heat-born condensation, the light growing more orange with each turn. They were close now. The Hotlands were bleeding into the surrounding caverns, warmth curling at their ankles like a silent warning.

A tremble ran through the ground. Subtle, but deep—like the stone beneath their feet had just taken a breath.

Everyone stopped.

Papyrus froze mid-step, one hand clutched dramatically at his scarf. Undyne’s eye narrowed. Alphys hesitated, her tablet angled sharply toward the floor like she was waiting for it to explain itself. Even Frisk turned on their heel, half a sign already lifted before they caught themselves, falling into silence with the rest.

It wasn’t violent. Just enough.

A breath. A pause. Then stillness again.

All eyes drifted to Alphys.

She blinked behind her glasses, the blue glow of her screen flickering uncertainly against her face. “It’s—um. It’s not—it’s probably not a critical fault. Probably.” She swallowed. “Maybe some… baseline instability in the sub-layered mantle strata where the CORE’s wiring intersected with—uh. Environmental erosion. I mean, it’s definitely—”

Her voice folded under the quiet.

Sans, who had stayed back just slightly from the group, stepped forward.

“ain’t nothin’ to freak out about,” he said, voice light, hands tucked into his pockets like always. “we’re probably just feelin’ harmonic feedback loops through the thermoelectric conduits. you know—residual oscillations from post-barrier structural imbalance. when the surface pressure equalised, it likely forced retrograde sympathetic pulses through the entire hotlands reactor network. kinda like when you flick a tuning fork next to another one and it starts ringing.”

He shrugged.

“textbook stuff.”

Papyrus blinked at him.

“BROTHER.”

“yea?”

“I UNDERSTOOD NONE OF THAT.”

Sans chuckled. “means the ground has the heeby jeebies. don’t worry ‘bout it.”

Papyrus let out a tremendous sigh of relief. “PHEW! AND HERE I THOUGHT WE WERE ABOUT TO BE SWALLOWED INTO A LAVA-FILLED CHASM.”

“nah,” Sans said, patting his shoulder. “not yet.”

They kept walking.

The further they went, the more the oppressive warmth began to settle into their bones. The Hotlands didn’t blaze so much as press—a thick, damp heat that clung to skin and soaked into cloth. The tunnels changed with it, stone giving way to blackened iron walkways, and the air tasting of ash and metallic steam. Veins of lava pulsed below some of the grates, red and slow and full of old power.

Undyne grimaced as she wiped sweat from her brow with the back of her glove.

“Ughhh. I hate this part. Every time I think I’ve adjusted, the humidity slaps me in the face again like a wet towel of doom.”

Papyrus nodded, ever cheery despite the heat. “IT IS RATHER TOASTY! LIKE LIVING INSIDE A BAKING PAN. OR A REALLY AMBITIOUS SAUNA.”

Frisk signed something with a smirk, then switched to voice as the air thickened.

“Maybe we should’ve brought sunscreen.”

“YOU JEST,” Papyrus said, “BUT LAST TIME I FORGOT TO BRING OIL FOR MY JOINTS AND MY KNEES SOUNDED LIKE A BROKEN XLYOPHONE.”

Undyne barked a laugh. “Oh man, I forgot about that! It was like skritch-bwong-kzzk every time you took a step.”

He beamed. “I WAS A MUSICAL MARVEL.”

They passed under one of the old pylons, its faded warning signs still clinging to bent frames. Somewhere beneath them, magma churned in slow circles. The silence between conversations deepened slightly. Everyone was sweating. Even Alphys, whose lab coat had long since been tied around her waist, looked like she was trying not to think about the next half-mile.

Undyne broke the silence with a grunt.

“So,” she said, tipping her head toward them, “how’s everyone’s jobs goin’? Been a while since we did the ol’ career check-in.”

Papyrus perked up immediately.

“MY JOB IS A DELIGHT! I AM CURRENTLY EMPLOYED AT LUIGI’S SPAGHETTABOUTIT!—A VERY FANCY HUMAN RESTAURANT WITH A WHOLE WALL DEDICATED TO PASTA HISTORY.”

“oh yeah,” Sans chimed, “that place rocks. and pap’s a hit. you should see the tip jar. it sparkles.”

Papyrus puffed out his chest. “IT IS TRUE. I HAVE BEEN TOLD THAT MY UNBREAKABLE POSITIVITY AND IMPECCABLE CUSTOMER SERVICE BRING JOY EVEN TO THE RUDEST OF HUMANS.”

Frisk gave him a thumbs-up.

'You’re really good at it.'

He glowed brighter than the lava vents.

“THANK YOU, HUMAN-FRIEND-FRISK. I TRY TO ADD A FLOURISH TO EVERY ORDER. I HAVE BEEN PRACTICING THE ART OF TRAY BALANCING, THE FLUIDITY OF WINE POURING, AND, MOST IMPORTANTLY—THE DRAMATIC PRESENTATION OF THE BILL.”

Undyne laughed so hard she had to stop and lean against a rail.

“You present the bill?”

“WITH A FLOURISH AND A FINAL ‘NYEH HEH HEH.’ THE HUMANS LOVE IT.”

Sans gave a proud nod. “told ya. best guy for the job.”

“Yeah, well, some of us still have boring jobs,” Undyne said, rolling her eye toward Sans. “How ‘bout you, bone-boy? You still hustling jokes behind the bar or what?”

“eh,” Sans said, scratching the back of his skull. “still do some stand-up at grillby’s, yeah. and lately i’ve been subbing at the local elementary when they need help for science.”

Alphys looked up at that. “Wait, really?”

“sure,” he said with a shrug. “i mean, it’s just the basics. gravity, inertia, thermodynamics, how to safely mix soda and mints without launching a bottle into orbit or sending a  kid home with missing limbs.”

Undyne stared.

“You? Teaching science?”

“yep.”

“I thought Alphys was the only nerd in our group.”

“HEY!” Alphys yelped. “I—well—okay, rude, but not wrong.”

Sans just smirked.

Papyrus, however, tilted his head curiously.

“BROTHER,” he said. “I FORGOT YOU KNEW SO MUCH ABOUT THAT STUFF.”

Sans paused.

His grin twitched. Not faded—just… shifted. More fixed. Like it had been pinned in place by something.

“yeah,” he said, more quietly. “me too.”

The others didn’t notice the change. Papyrus had already gone on to mention a funny customer at the restaurant who tried to fight the chef, and Undyne was mocking him with fake kung fu noises. Alphys tapped something into her tablet. Frisk walked a little closer, glancing up at Sans with that same quiet curiosity they always had when something didn’t quite click.

Sans didn’t meet their eyes.

He just kept walking.

Somewhere beneath them, the CORE stirred again—barely audible, a whisper of motion that didn’t quite reach the surface. The heat pulsed.

Frisk looked ahead.

They were almost there.

Chapter Text

Alphys was knee-deep in wires and circuit casings, her rubber-gloved fingers trembling slightly as she ran them across the underside of a large generator terminal embedded into the wall of her lab. The place was quiet save for the low hum of dormant machines and the occasional flicker of an overhead light — more subdued than usual, more fragile. She’d done this checkup a thousand times before, but things were different now. The power readings weren’t matching up with the baseline she remembered. Not dangerously off, not yet, but still... enough to make her stomach tighten.

She straightened, pushing her glasses up her nose with the back of her wrist and squinting at a web of thin cracks spidering just beneath a panel casing. Nothing major. Cosmetic, maybe. Probably. Still, she muttered a low, annoyed sound under her breath and scribbled something into the small, weathered notepad she always kept on hand. The pen made that dry scratchy noise it always did when she was writing too quickly. She didn’t even realise her shoulders were drawn up until she felt the first dull ache bloom behind one of her shoulder blades.

Somewhere behind her, a muffled voice spoke — probably Undyne. Alphys turned, readjusting her coat, and took a glance across the room. The others were scattered across the old lab, each one drawn to something different.

Undyne stood by the far wall, her arms folded as she stared up at a fading Mew Mew Kissy Cutie poster taped high above a filing cabinet. The edges had browned with age, the corners curled from heat and time. Even from here, Alphys could tell the glue had all but turned to dust. It wouldn’t survive the trip to the surface. If anyone tried to pull it down, it would probably crumble. Undyne must’ve known that — she didn’t touch it. Just stared at it, jaw tight, a strange look caught between nostalgia and reluctant acceptance playing across her face. Then she shook her head with a small scoff and turned away.

Alphys’s gaze drifted to the central table, where Papyrus and Frisk were crouched together, their heads nearly touching as they examined a tangle of dusty blueprints. Mettaton’s schematics. There were scribbles in pink ink all over the margins — MTT’s distinct flair. Curved lines. Hearts. Dramatic arrows and crossed-out phrases with new ones written in grand cursive. Frisk made a gesture with one hand — a quick little flick of their fingers — before glancing over their shoulder to make sure Alphys had seen. They smiled when they caught her eye, and signed, "This one looks like a disco cannon."

Papyrus gasped with appropriate theatricality. “A DISCO CANNON?! DO YOU THINK METTATON WOULD HAVE LET ME USE IT IN THE DINNER SERVICE PORTION OF HIS SHOW?!” He held up the blueprints like a sacred tablet. “OH, THE POSSIBILITIES!”

Frisk responded with a giggle and a nod, switching to verbal speech, “Only if it shot glitter. Glitter’s the only acceptable form of culinary warfare.”

Papyrus beamed. “YES, YES! EXACTLY! GLITTER, AND POSSIBLY LASAGNA!”

Frisk’s brows lifted. “Lasagna?”

“FOR DRAMATIC EFFECT!”

Across the room, Sans was hunched over a shelf in the corner, squinting at some of Alphys’s older notes — the sort of scrapped sketches and calculations she hadn’t looked at in years. Some of it was early work on dimensional stability, some of it half-formed diagrams for machines never built. She didn’t even remember putting those up there. Just a few old formulas and systems left to gather dust.

He caught her watching and drifted over with a lazy sort of casualness, one hand still buried in his hoodie pocket. His sockets were shadowed, expression unreadable.

“find anything fun?” he asked, jerking his head back toward the shelves.

She adjusted her glasses again. “Nothing I didn’t already know was there... you?”

“nothin’ outta the blue,” he said. “but might be good to shut off what we can. just in case.”

Alphys frowned. “You know I can’t just pull the plug on everything, Sans. There are still monsters living here. If I cut power to half the lab, it could black out whole sectors of the lower city. They depend on the energy grid.”

He nodded, rubbing the back of his skull. “yeah. i get it. wouldn’t be fair.”

There was a pause. Then he shrugged, the bones in his shoulders shifting in that loose way they always did. “we’ll figure somethin’ else out.”

Alphys didn’t say anything right away. The air between them buzzed faintly with the hum of a capacitor across the room.

“I can recalibrate some of the smaller relay systems manually,” she said at last. “If I reroute power around the damaged circuits, I might be able to ease some of the strain without killing the grid.”

“sounds like a plan,” Sans replied. He clapped her on the shoulder gently — a small gesture, grounding. “lemme know what you need.”

She nodded, then turned back toward the others as they all began to regroup. The energy in the room shifted as Undyne approached, her eyes flicking from Frisk’s hands to Papyrus’s wild gesturing to the way Alphys hadn’t stopped biting at the inside of her cheek.

“So,” Undyne said, wrinkling her nose as she glanced at a half-melted conduit pipe near the floor. “Remind me again why we’re not just dragging all this junk topside?”

“It’s not junk!” Alphys snapped before she could stop herself. “It’s... legacy. Mettaton’s things, my research, power routing — it still serves a purpose down here.”

Undyne raised an eyebrow, but didn’t push. Her arms crossed, one clawed finger tapping against her bicep in a twitchy rhythm. She huffed, loud and exasperated, the sound echoing through the dim underground chamber like a disgruntled steam valve. She'd been thoroughly chastised earlier for attempting to suplex Frisk—a misunderstanding, in her opinion. The kid had been nimble enough to dodge, and anyway, the move hadn’t even landed. But apparently the potential to flatten several thousand bits of ancient, unstable tech was enough to earn her a sharp scolding and a stern look from Alphys.

Now she rolled her eye, exaggerated and dramatic, before slumping back against the nearest concrete wall. Her scaled back scraped lightly against the rough surface, her boots tapping idly against the floor. “I could be fighting criminals right now,” she muttered under her breath, dragging the sentence out like it physically hurt to say it. “Big bads. Thieves. Vicious, lawless surface goons.” Her voice echoed, tinged with irritation. “Instead I’m playing babysitter to dusty wires and ancient blueprints.”

From her corner, Alphys didn’t even look up from her tablet. Her voice came flat and unimpressed. “You’re on work leave because you put someone in the hospital.”

“That was one time!” Undyne protested, throwing up her arms. “And it was paid leave!”

Alphys didn’t respond. She adjusted her glasses and scrolled through the diagnostic readout, her stylus clinking softly against the touchscreen as she ran it over her notes. Beside her, the aging hum of the generator filled the silence between them—a low, thrumming buzz that had become so constant it practically faded into the backdrop.

Frisk giggled softly, a sound halfway between amusement and disbelief, before returning their attention to Papyrus, who was animatedly discussing the structural impracticality of Mettaton’s original EX chassis. His bony fingers flitted across the dusty blueprints like he was giving a lecture to an audience of hundreds.

Frisk, leaning forward with elbows on the cracked plastic table, signed something with a flick of their hands. "Too many limbs. Even spiders don’t walk like that."

Papyrus gasped with theatrical offense. “HOW DARE YOU!” he cried, completely ignoring the rumble of ancient power lines above them. “METTATON’S DESIGN WAS BEAUTIFUL! A SYMPHONY OF FORM AND FUNCTION! GRANTED, YES, THE JET BOOSTERS WERE A BIT EXCESSIVE, BUT THEY WERE A NECESSITY TO THEATRICAL MOVEMENT!”

Frisk laughed, a little wheeze slipping out as they clapped their hands together once in mock surrender. “Alright, alright,” they said aloud, voice light. “He was... fabulously inefficient.”

“You are impossibly rude,” Papyrus declared, though his grin made it clear he wasn’t truly offended. He turned to say something else—

—and the ground trembled.

It wasn’t as harsh as the first one. More subtle, like a sigh of the rock around them. But it was still enough to silence the room.

Papyrus paused mid-sentence. His fingers curled against the paper. The slight rattle of a hanging light fixture ticked in the space above them, the sound thin and uncertain.

Undyne’s stance shifted, her back leaving the wall as she moved instinctively into something a little more alert. Her hands clenched, one eye narrowed.

Alphys straightened too, and she wasn’t even trying to hide the way her eyes darted to the ceiling, then to her equipment. The screens remained steady. No red alerts. No diagnostics flashing into chaos. Just that same slow pulse of power and old code.

Frisk tilted their head. Their hands hovered mid-air, fingers twitching in a question that never formed.

Papyrus, for once, was quiet.

And then—he spoke.

"...Did you hear that?" His voice came small, almost uncertain. A note of something in it that hadn’t been there before.

Frisk frowned. “Hear what?”

But he didn’t respond right away. His posture was oddly still, head tilted as if listening to something just out of reach. His gaze wasn’t directed at anyone. Not his friends. Not the machines. Not even at the Mettaton schematics crumpled under his palm.

It was like he was hearing something they couldn’t.

“Pap?” Frisk tried again. Their hands hovered, ready to sign, but unsure of what to say. “What is it?”

“No one else heard it?” Papyrus asked again, this time more quietly.

“Didn’t hear anything,” Undyne said bluntly. She walked over and gave the floor a light stomp. It echoed back, flat and dull.

“I didn’t register anything,” Alphys added, flicking her tablet screen toward the last seismic reading. “No vibrations, no drops in power—well, no significant ones. I’ve got a minor flux near generator two, but it’s nothing that would cause sound.”

Sans appeared at her side a second later, silent as always when he didn’t feel like drawing attention to himself. He looked at Papyrus, long and unblinking. “What’d it sound like?”

Papyrus hesitated. His expression didn’t change much—just the smallest crease between his brow bones, the slightest shift in his jaw. He looked at each of them in turn, then glanced back toward the far hallway where the collapsed portions of the lab stretched into dimness.

“I don’t know,” he admitted softly. “I can’t remember.”

Alphys and Undyne exchanged a look. It was a small thing, but it passed between them like a current.

“Maybe it was nothing,” Frisk offered, voice light but uncertain.

Papyrus nodded absently, but it was clear his mind had already drifted elsewhere.

Undyne clapped him on the back with enough force to rattle his bones. “You’ve been down here too long, Bones. The air’s stale. Might be getting to your head.”

“I DON’T GET HEAD FOG,” Papyrus insisted, but the usual bravado was muted. He looked back toward that hallway again, like he was expecting something else to come from it. But nothing did.

Sans let the moment settle, then looked at Alphys. “Still think it’s safe to keep everything running?”

Alphys exhaled through her nose. Her arms crossed tightly over her chest. “I don’t know anymore,” she said quietly. “But until we know for sure, we can’t risk shutting the whole system down. Not without warning the others. Not without preparing the grid.”

Sans nodded once. “Alright. Guess we’ve got more snoopin’ to do.”

Frisk stood too. They signed: "Where should we start?"

Alphys tapped her chin, then pointed down the far tunnel—the same one Papyrus had looked toward.

“If there’s an issue, it’s probably down that way. Most of the residual power is funnelling through Substation Three. It wasn’t exactly stable before.”

Undyne immediately drew her spear—non-lethal energy mode—and gave a small grin. “Finally. Something I can poke.”

Frisk signed: "Let’s go slow. No breaking things."

Undyne pouted. “You’re no fun.”

“I’m fun and precise,” Frisk replied with a shrug, switching fluidly between signs and speech.

Alphys stayed behind at the console, fingers flying over the keys as the others began to make their way down the corridor. Sans drifted behind them, hands in his hoodie pocket, gaze sharp.

Papyrus lingered at the entrance of the tunnel, one hand gripping the edge of the doorway. He turned his head slightly.

And for just a moment, before he followed, he thought he heard it again.

A faint scrape.

A breath.

Something moving, just out of view.

He looked.

There was nothing.

But it didn’t feel like nothing.

He stepped forward anyway.

Sans eyed his brother carefully as they moved together, his pace intentionally unhurried so as not to push him. Papyrus walked with his usual long strides, but the bounce in his step was missing. There was something stiff about the way he held himself, like a wind-up toy running low on tension. Sans didn’t say anything right away. He just moved beside him, hands shoved deep in his hoodie pockets, one step for every two of Papyrus’, his sockets tracking the taller skeleton’s posture more than his path.

Ahead of them, Frisk, Undyne, and Alphys led the way down the main hallway that branched off from the central chamber. They were heading toward the corridor that eventually dipped into the entrance of the True Lab—though that part had long since been sealed with reinforced barriers and a mess of redundant locking protocols Alphys had insisted on. The hallway wasn’t in much better shape than the lower labs; flickering lights buzzed overhead and cast long shadows that jittered with every footstep. The concrete floor cracked here and there, splitting into veins of dust where time and pressure had eroded the surface. Rooms lined either side—ancient storage closets and server hubs, most with their doors rusted open or hanging on broken hinges.

Alphys paused at one door, her glasses catching the half-dead glow of the light above as she scanned her notes. “This one,” she muttered, then pushed it open and slipped inside, Undyne close behind and Frisk right on their heels.

That’s when Sans stopped.

He reached out with a single hand and lightly touched his brother’s sleeve, just a graze—barely anything, but it was enough. Papyrus halted, startled, as though the contact had pulled him back from some internal fog.

Sans tilted his head. “You good, bro?”

Papyrus blinked at him. His eyesockets were wide, but not in the dramatic, over-expressive way he usually wore them. No bold proclamations or excited gestures. Just a quiet tension around the edges of his expression. He opened his mouth, clearly about to say something—then stopped. His shoulders stiffened.

“I—OF COURSE,” he said, the words forced a little too quickly. “I AM PERFECTLY FINE, SANS. I AM MERELY—WELL—SLIGHTLY CONCERNED ABOUT THE STABILITY OF THESE CORRIDORS. NOTHING MORE.”

Sans didn’t move. Didn’t blink. Just stared at him in that infuriatingly blank way he had—the way that said he didn’t believe a word of it, and that Papyrus knew it.

Papyrus sighed. It was a sound dragged from somewhere deep inside, the kind of sigh that deflated his entire posture. He lifted one gloved hand and rubbed at the other, twisting the fingers slowly as if trying to work something loose in the fabric—or in himself.

“I…” His voice dipped lower, no longer pitched up into bravado. “I’m not okay, Sans.”

That alone was enough to make Sans straighten slightly.

Papyrus didn’t look at him as he spoke. He kept his gaze on his hands, fingers still wringing. “I didn’t want to worry anyone. Everyone’s already tense. But… when that tremor happened—the second one—I… I heard something.”

Sans’ eye sockets narrowed, though his expression didn’t otherwise change. “What kinda something?”

Papyrus shook his head, frustrated. “That’s the thing. I don’t know. I heard it, and then I forgot it. Like it was yanked out of my head before I could hold onto it. I remember the feeling of hearing it. That’s all.”

Sans stayed quiet, waiting.

“It was during the last shift. Right after the rumble. You were all talking, and I was going to say something, but… I couldn’t remember what it was. And now it’s bothering me. Like I left the oven on. Only instead of a lasagna, it’s… something worse. Something I’m not supposed to forget.”

He finally looked at Sans then, and there was something raw in his sockets—something Sans hadn’t seen since the Reset days. Fear.

Sans dropped his gaze briefly, then back up. “You think it’s connected to the tremors?”

Papyrus nodded once. “Yeah. I do.”

“Alright.” Sans’ voice was low, steady. “Then let’s figure it out. One step at a time.”

Papyrus nodded again, slower this time. He wasn’t comforted—not really—but there was something grounding about having Sans here, in this moment, when he didn’t feel entirely like himself. When his memories felt like lace through his fingers.

They stepped into the room after the others, the door creaking shut behind them with a metallic groan.

Alphys flicked the switch on the monitor for the third time, teeth grit behind a half-formed grimace. The machine groaned like a tired beast, screen flickering faintly with grey static before dying again. Her claws tapped irritably against the rusted casing.

"Come on," she muttered, hitting the power toggle again with a little more force than necessary. The screen buzzed once more, then fizzled out entirely. She let out a short huff, turning toward the group behind her with an apologetic slump in her shoulders. “It’s not working. Ugh, the power must be—yeah, it’s cut to this whole section.”

Frisk, who had been peering curiously over her shoulder, signed quickly before speaking aloud, “Is there a way to fix it?”

Alphys scratched at the side of her neck, clearly not thrilled to deliver her next line. “The main generator runs through the True Labs. If we wanna get this stuff powered again, that’s the place we need to check.”

That name dropped like a stone into the room’s atmosphere. The True Labs.

It was subtle, but palpable: Papyrus straightened just a little too stiffly, Undyne shifted her stance like she was bracing herself, and Frisk’s fingers curled slightly at their sides. Even Sans’ usual lazy lean straightened by a hair’s breadth. No one said anything for a few seconds—just the hum of the emergency lighting, flickering overhead like a dying heartbeat.

The memory of the amalgamates—those twisted, melting souls, all memory and agony—still lingered like cold breath on the back of the neck. Alphys had done what she could, after it was all over. Reunited them with their families, those who could bear it. Some had met them with open arms and relief beyond words. Others… hadn’t. The mixture of grief and horror wasn’t something anyone liked to dredge up.

Alphys cleared her throat awkwardly and looked down at her feet. “T-the entrance is still blocked off anyway. After everything, I locked it down. It’s—well. Safer that way.”

“Or,” Sans offered casually, stepping closer, “I could just shortcut in. Hop down, check it out, hop back.”

His voice was light, but the suggestion wasn’t. Everyone turned to look at him.

Alphys’ brow furrowed. “I mean, yeah, that—might work. B-but Sans, it’s dangerous down there. Even if most of the old systems are dead now, there are still environmental hazards. Unstable equipment. Old containment doors. Just—”

“I’ll be fine,” he said with a shrug, his grin in place but his eyes unreadable.

Undyne snorted, arms crossed. “With your HP? I’m not letting you just waltz into the creepiest place in the Underground alone.”

“Oh?” Sans drawled, the corner of his grin ticking up. “Didn’t know you cared so much, Undyne.”

She scowled and took a step forward. “I don’t. I just don’t want to have to explain to anyone how you got pancaked by a falling support beam or turned into soup by malfunctioning security lasers or whatever else could go wrong down there.”

“Aw, I feel very loved,” Sans said, mock-sniffling. “Real emotional moment here.”

Undyne rolled her eyes, but there was a tension behind her stance that didn’t relax. “Yeah, well, save the drama for your brother. I’m coming with you.”

Sans tilted his head slightly, eyeing her. “You sure? I thought you were on paid work leave.”

That earned him a low growl from the fish-like warrior. “Yeah, well, I’ll consider this community service.”

“Gotta say,” Sans mused, glancing at Alphys, “this wasn’t exactly the field trip I had in mind today.”

Alphys shifted uncomfortably. “L-look, if you really have to go, at least take a reading device with you. If the generator’s blown, I need to know why. Just turning it back on won’t mean anything if it fries again five minutes later.”

Frisk, who had been quiet through the exchange, slowly stepped toward the two. Their gaze was fixed on the floor, brow slightly furrowed in thought. Their fingers signed, 'Do you need me to come too?'

Papyrus, silent until now, lifted his head quickly. “NO!” He caught himself and quickly added, “I MEAN—NO, I DON’T THINK THAT WOULD BE WISE. YOU—YOU’RE THE HUMAN AMBASSADOR, AFTER ALL. YOU HAVE VERY IMPORTANT RESPONSIBILITIES.”

Frisk tilted their head at him, one brow arched in polite skepticism.

“I’M JUST SAYING,” Papyrus continued, a little too quickly. “MAYBE STAYING OUT OF THE SUSPICIOUSLY CREEPY LABORATORY IS THE BEST IDEA FOR YOU.”

Frisk didn’t argue. But they stepped closer to Papyrus anyway, giving his scarf a gentle tug. He glanced down, and their eyes met. Then Frisk raised their hand and signed again.

'You’ll tell me if something’s wrong, right?'

Papyrus hesitated. Then, slowly, he nodded.

The moment passed. Undyne cracked her knuckles, clearly impatient to be doing something other than standing around. “Alright. Let’s get this over with. The sooner we get that generator back online, the sooner we can stop lurking around in this haunted house.”

Sans exhaled through his nose, the closest thing he gave to a sigh. “You’re really selling the experience, Undyne.”

Alphys handed Sans a small tablet, barely functional but able to pick up the necessary diagnostic signals. “Just… be careful. Please.”

He didn’t joke that time. Just nodded.

Then, with a flicker of blue light, he opened a shortcut. The space warped with a soft rush of displaced air and folded in on itself. He and Undyne stepped through—and the gap closed behind them with a snap.

Papyrus stared at the place they had vanished for a long moment, his expression unreadable.

Beside him, Frisk reached for his hand.

He didn’t let go.

Down in the lower levels,

Undyne shivered as they stepped into the yawning dark of the True Lab’s outer corridor. “Ugh,” she muttered, arms folding over her chest, her shoulders bunching slightly. “I’ll never get used to teleporting. Feels like my guts are playing jump rope.”

Sans grinned, unbothered. “just takes practice,” he said, and held out the diagnostic tablet Alphys had handed him. Its flickering screen was barely brighter than the dim red of the emergency lights embedded in the ceiling. Still, it cast a weak, blue-tinted glow that gave their surroundings an eerie, underwater feel. “although, if you’re still getting nauseous after the seventh hop, maybe you’re just not cut out for short-range warping.”

Undyne made a face. “Trust me, I know I’m not.”

Then, with a flick of her wrist, she summoned a few spears of pale, cyan light. They hovered in the stale air overhead, their points directed upwards, casting long, angular shadows across the corridor walls. The light glimmered faintly off rusted metal and yellowed tiles.

“Here,” she said, jerking her chin toward them. “So you don’t walk into a wall and break your skull. Again.”

Sans chuckled. “one time.”

“Once is all it takes,” she replied, though her smirk said she wasn’t that mad about it.

He nodded a thanks and began walking, the soles of his slippers brushing almost silently against the dusty floor. He kept the tablet angled upward, using it like a flashlight. As they passed the first junction, he paused. His sockets drifted to the right.

Empty beds lined the wall of the adjacent room—half-covered in tattered white sheets, their thin mattresses discoloured and sunken from long disuse. Wires and tubing dangled from machines like dead vines, looping around IV poles and knocked-over monitors. The room hadn’t been used in years. Still, the air smelled faintly of antiseptic and old sorrow.

Undyne followed his gaze. Her footsteps slowed.

“I don’t think I’ll ever forget what happened down here,” she said softly, arms at her sides now, her posture no longer that of the ironclad warrior she always tried to be. Just a soldier, standing in the wreckage of an old war no one won.

Sans didn’t answer at first. His eyes lingered on one bed in particular—its frame bent inward, like someone had thrown something heavy into it. Or someone had fought against the restraints. There were scratches on the floor tiles. Not the kind that came from shoes. Claw marks.

After a long breath, he asked, “you agree with what alphys did?”

Undyne’s jaw shifted. She turned her head, eyes narrowing a little, not quite looking at him. “She didn’t mean for any of it to go the way it did.”

“didn’t say she did.”

“Well, what’re you getting at?” she snapped, a little sharper than she intended. “You trying to start an argument down here?”

“nah,” he replied evenly, already turning away from the room and back toward the corridor. “just curious.”

She frowned. After a moment, she followed, falling into step beside him.

“You don’t bring something like that up unless you have something to say,” she muttered.

Sans was quiet for a few paces. Then he said, softly, “if it were papyrus. if he’d fallen down… and someone told me he could be fixed… and i said yes, and he came back like that—half aware, confused, hurting all the time…”

His voice trailed off.

He didn’t need to finish the sentence.

“I don’t think i could live with myself,” he said finally.

Undyne exhaled. Her grip on her remaining summoned spear tightened just a little.

“I get it,” she said. “I do. And I—I won’t pretend I wasn’t furious when I found out what she’d done. I mean, she hid all this. Lied to everyone. You remember how close we were to falling apart after the truth came out.”

“yeah.”

“She tried to resign, you know. The day after the evacuations.” Undyne huffed, lips quirking in bitter memory. “Gave me this whole speech about accountability. Said she deserved to be locked up, not given more chances.”

“what’d you say?”

“I shook her by the shoulders... hard,” Undyne said with a snort. “Told her if she really wanted to make it right, she’d stick around and fix it.”

Sans chuckled, though it was faint. “harsh.”

“She needed to hear it.”

“yeah,” he admitted, glancing sideways at her. “but… you ever wonder if this place should’ve just been left buried?”

They reached a corner in the corridor and turned down another hall, darker still. The air was colder here. The walls slick in some places, like moisture had crept in through cracks long ago.

Undyne’s remaining light spears floated closer to the ceiling, casting them in a deeper blue hue.

“Every day,” she said at last. “But it wasn’t buried. And if it exists, then we have to face it. Fix what we can. Learn from it.”

“learning doesn’t undo what happened.”

“No,” she agreed. “But not learning makes sure it happens again.”

They walked in silence after that.

The generator room wasn’t far. Sans glanced occasionally at the tablet, watching the readings—voltage, power distribution, residual magical interference. Most of the numbers didn’t mean anything to him, not the way they did to Alphys, but he could at least tell the thing was completely offline.

Lights up ahead marked the entrance to the generator core. Several had blown out, but a few pulsed with dim life, like tired stars on their last flicker. The double doors to the room were slightly ajar, and a thick black cable snaked out from the gap, looping across the floor like a dead vine.

Sans reached forward, pushing the door open with a low groan.

And immediately froze.

The room was quiet. Still.

But not empty.

Undyne paused mid-step, her breath catching in her throat as she caught sight of Sans—completely still, gaze locked, shoulders tensed like a coil wound tight. His expression had gone blank, the slight slackening of his features unfamiliar and deeply unnerving. It wasn’t like him to freeze up, especially not here, not with her right beside him.

Her eye tracked the direction of his stare instinctively, hand hovering near her shoulder in case she needed to summon a spear. But the space he was looking at—just an empty corner beyond the backup generator’s housing unit—was completely unremarkable. Dust coated the floor. Nothing moved. Nothing stirred.

She narrowed her eye. “Sans?” she called out, voice low but firm.

No answer. Not even a flicker of acknowledgement.

She stepped closer, hesitating for just a second before reaching out to pat his shoulder. “Hey, bones—”

A bone shot past her.

It was so fast it left a white blur in her vision and embedded itself into the metal wall behind her with a harsh, screeching clang. Sparks spat outward. The recoil of the impact vibrated through the room, echoing up through her boots.

She jumped back, instincts kicking in hard. Her arm raised automatically, a spear materialising in a tight grip. She turned sharply, ready for a fight—only to find Sans staring at her.

His left eye was blazing a brilliant, unnatural blue.

For a moment, it was like he didn’t recognise her. His sockets were wide, darting between her and the space he’d been fixated on, confusion blooming slowly over his features like a tide of slow-moving ink. The glow in his eye dimmed. He blinked a few times, and then the tension in his body eased all at once—like strings being cut.

Undyne lowered her spear, cautiously. “What the hell was that?”

Sans rubbed at the back of his skull, fingers trailing down the edge of his hood. He looked away, the nonchalance in his shrug only half-real. “thought i saw something but… forgot what.”

She frowned, lowering her voice. “That’s exactly what Papyrus said.”

He stilled again, just for a breath. Then exhaled and took a step forward toward the generator without responding.

“You alright?” she asked, watching him carefully.

He nodded, not looking at her. “we’re already down here. no point in backtracking now.”

She crossed her arms. “That’s not what I asked.”

Sans looked over his shoulder. There was a flicker of something behind his expression—like a thread being pulled too tight, threatening to unravel if he tugged even slightly harder. He offered a small shrug again, then turned back toward the wall panel housing the backup generator’s main circuit interface. “probably just nerves. not exactly the coziest place, you know?”

Undyne didn’t buy it. Not for a second.

She moved to stand beside him, eyes narrowing slightly. “First Papyrus, now you,” she said, folding her arms. “Is there something you two aren’t telling the rest of us?”

Sans stilled again, tapping a few keys on the touchscreen. Lines of code flickered up, the diagnostic screen quickly adjusting to reflect his input. He didn’t look at her. “it’s nothing. we talked.”

“‘Nothing’ doesn’t make people forget what they’re seeing. Or shoot bones at their friends.” Her tone wasn’t sharp, but it was hard. Concern and suspicion wrapped tightly around every word.

He didn’t respond. And she knew him well enough to recognise the shut-down when she saw it. Pressing would go nowhere. So she let the moment stretch, then slowly unclenched her fists.

“How long is this gonna take?” she asked instead, sighing.

“few minutes,” Sans said, peering at the flickering screen. “loading bar’s at sixty-two percent. should kick in soon.”

He leaned his weight back slightly, hands in his pockets as he watched the progress bar jump forward. It flickered to sixty-six percent with a mechanical hum from the generator, then slowed again, shuddering slightly with each step.

Undyne paced a slow circle behind him, her gaze drifting across the shadows that lined the walls, half-painted with flickering emergency light and the pale gleam of her floating spears. Everything about this place set her teeth on edge. The walls seemed too narrow, the ceiling too low. The silence was too deliberate. It was the kind of quiet that didn’t just happen—it waited. Coiled.

“Do you really think this thing’s gonna hold?” she asked, breaking the silence. “It’s been years since anything down here’s had maintenance. One wrong spark and this whole level could go up in smoke.”

“nah,” Sans murmured. “this unit’s separate from the power grid that fried during the CORE incident. it was built to run cold. not a lot of magic in its casing—runs on base current. kind of old-fashioned, really.”

She arched a brow. “You sound like Alphys.”

“she’s been talking at me a lot,” he deadpanned. “eventually some of it sticks.”

Undyne gave a short laugh. It wasn’t exactly amused.

Her gaze drifted back toward the corridor behind them, where the dark swallowed the path like a throat. She hated the way it seemed to watch them—like they were being tolerated, not welcomed. Like the lab itself was still aware, even after everything had been cleared out, even after the amalgamates had been taken home.

Some found peace. Some didn’t.

She remembered the way some of the families had screamed when they saw what their loved ones had become. How others had tried to hug them and pretended not to notice the melted flesh or the jittering voices layered in overlapping loops.

She remembered standing next to Alphys, who was shaking so hard her glasses had fallen from her face. Undyne had picked them up for her. Held them in her hand. But the scientist hadn’t looked up. Couldn’t.

“Hey,” Undyne said now, voice low, still watching the corridor. “You said you talked to Papyrus?”

“yeah.”

She gave him a sidelong glance, sharp and expectant. “What was it about?”

Sans didn’t answer at first. His shoulders shifted slightly, a tiny shrug that betrayed nothing. The screen in front of him continued to whirr, the loading bar holding at 67%, blinking patiently.

She elbowed him lightly. “Well? Or am I gonna have to make it an order, Cap’n?”

He exhaled, a huff that might’ve been a laugh. “is that an order, cap’n?” he echoed, voice dry.

She groaned, rolling her eye. “Seriously? Can you not be a smartass for five seconds?”

Sans let the silence linger just a bit too long before answering. “we talked about him forgetting stuff. weird gaps. things not adding up. we're gonna try and figure it out.”

Undyne’s eye narrowed, her expression tightening with the weight of something more than curiosity. “You think it could be... I dunno. A trauma response?”

Sans visibly winced, his head pulling back like she’d offered to chew on glass.

“Come on, Sans,” she pressed, her tone sharpened by frustration but not cruelty. “You and your brother never talk about your past. Ever. And I’m starting to think that’s not just because you don’t feel like it.”

He didn’t say anything, but his fingers stilled against the keyboard, mid-motion. His left eye, still faintly glowing from earlier, dimmed a bit.

Undyne took a step closer, her posture firm but not aggressive. Not yet.

“I mean it,” she continued, tone softening only slightly. “You guys just... showed up in Snowdin. Right? That’s what the inn owner told me. One day, you’re there. No warning. No family. No other skeletons. And Papyrus—he’s told me a little. Bits and pieces. Enough to know your childhood wasn’t exactly great.”

Sans tilted his head, finally looking at her. Not irritated. Not defensive. Just watching.

“You can’t just keep brushing this stuff off forever,” Undyne added, voice gentler now. “It’s not just about him anymore. It’s you, too. And you look like hell, Sans.”

He blinked slowly, like she’d pointed out the weather.

“relax,” he said, calm but not dismissive. “you’re overthinkin’.”

“I’m frustrated,” she corrected sharply. “Frustrated that you two are always so damn secretive. You know where I came from. You know how Gerson raised me. You know how I lost my eye, how I had to train myself up from nothing. But me? What do I know about you two?”

Sans raised a brow.

“I know Papyrus says ‘Sans raised me, so I take care of him now.’ That’s it. That’s all I ever got.”

The silence that followed didn’t stretch—it coiled. Tight and breathless.

Sans gave her a look. Not angry. Not amused. Not defensive.

Just a look that said: You done?

Undyne exhaled through her nose and shut her mouth.

The screen beeped softly, flickering to 74%.

“so... trauma response,” he said after a while, low and sardonic, but not mocking. “that your professional opinion, doc?”

Undyne crossed her arms. “It’s a guess. And a better one than pretending it’s just nerves.”

“never said it wasn’t real,” Sans muttered. “just... dunno what to call it yet.”

She leaned against the wall beside him, eye still flicking now and then toward the corridor as if half-expecting something to be lurking in the dark. “You’re scared,” she said finally. “You wouldn’t be snapping bones at empty air if you weren’t.”

“just a reflex,” he replied, a little too fast.

“Right,” Undyne said flatly.

The loading bar ticked upward again. 81%. The hum of machinery surrounded them, a steady thrum that seemed to vibrate through the bones.

Sans’s hand hovered above a cluster of keys but didn’t press them. He stared at the screen like it might bite him.

Undyne stayed quiet for a while, and when she spoke again, it was softer. “You know, I don’t want to push you. I’m not trying to make you dig up stuff you’re not ready to talk about. But... Papyrus is scared. You’re acting weird. And I’ve got a bad feeling in my gut. That usually means something.”

He glanced at her, jaw working behind his teeth like he was weighing something.

Then he sighed, rubbed at his browbone, and slumped slightly. “look. i dunno what’s goin’ on. i just know it’s not normal. it’s like...” He trailed off, fingers twitching in the air like he could pull the right words out of it. “like my brain’s got static. like something’s been erased, but the space where it was is still there.”

Undyne frowned.

“papyrus feels it too,” Sans went on. “he’s been sayin’ he remembers things wrong. or not at all. like there’s holes. stuff that should be there but ain’t.”

A pause.

“it’s like tryin’ to walk on a staircase that’s missing a step.”

They were both quiet after that.

Finally, Undyne said, “That sounds like more than nerves.”

“yeah.” Sans scratched the back of his skull. “but if it is something real, we can’t just leave it. that’s why i’m here.”

“What if it’s dangerous?”

He gave her a lopsided look. “then it’s a good thing you’re here too.”

That earned the smallest of smiles from her. “Damn right.”

The generator beeped again. 93%.

“i’ll finish up here,” Sans said after a pause. “can you keep an eye on the hallway?”

Undyne held his gaze for a moment longer than necessary, searching it for something—hesitation, uncertainty, maybe even fear—but all she found was that same bone-deep fatigue that had settled in his expression more and more lately. With a slow nod, she turned away from the desk and moved to the corridor entrance, spear in one hand, her weight shifting as she took up her post.

The hallway stretched out ahead, low-lit and draped in long shadows that clung to the walls like vines. There was no sound but the occasional soft electric hum from deep within the lab—something mechanical and unknowable ticking over in the dark. She squinted down the corridor, her single eye sweeping left, then right. Quiet.

Still, her grip on the spear tightened.

From behind her, she heard the subtle tap of keys and Sans shifting in his seat. She exhaled through her nose and didn’t turn back, just spoke softly into the silence.

“…Sorry,” she said.

Sans didn’t respond immediately.

“I mean for pushin’ you,” she clarified, glancing over her shoulder. “I just—”

“neither of us remember.”

Her arms slowly uncrossed at that, and she blinked, straightening up just slightly. She turned around halfway, leaning against the wall now, brow raised. “What?”

Sans’s back was still to her. He hadn’t moved from the screen, his shoulders still hunched in that lazy, deliberate way of his, but there was something about his posture now that had changed. Like something had settled in him. Or maybe cracked.

He twisted in his seat slightly, just enough to look back at her with a half-smile—wry, tired, a little bittersweet. “i mean it. me n’ papyrus—we got no memory of anyone raisin’ us. no parents. no family. no friends from before. nothin’. it’s just always been me ‘n him.”

Undyne didn’t say anything.

“our first real memory?” he went on, voice softer now. “was bein’ found by asgore. we were kids. paps was about eight. i was maybe twelve.”

She looked at him, her expression unreadable, then exhaled slowly and whispered, “Damn. That sucks.”

He let out a quiet chuckle, not cruel, not bitter. “heh. yeah. it’s weird, huh? but it’s just... the way it is. not really much to dig up. tried before. came up empty.”

Undyne hesitated, then stepped forward, her spear lowered now, her posture more open. “I’m sorry for pushing.”

Sans shrugged. “nah, don’t worry ‘bout it. figured paps would’ve told you, honestly. guess he didn’t.”

“No. He didn’t.”

“yeah. it’s not really something he likes to talk about. he gets weird about it sometimes. says it doesn’t matter. and honestly? he’s kinda right. not like there’s anything to remember.”

She nodded slowly. “But it does matter. Maybe not in a ‘fix it’ kind of way. But... it’s still a piece of you. Of who you are.”

Sans tilted his head thoughtfully, then gave a small smile—gentler now. “guess so. but it’s not like i lose sleep over it. just... some things are what they are, y’know?”

That hung in the air for a moment. Undyne watched him a while longer, then nodded again, slower this time, more understanding in the motion.

“So Asgore found you both?” she asked.

“yep,” Sans replied, swiveling back to the console. “wandering around near the Waterfall border, apparently. guess we looked like lost kids. i don’t remember any of it. one second it’s dark, next second, there’s light, and this big goat guy’s talkin’ to us like we’re his own.”

“Did he take you in?”

“yeah. didn’t hesitate. let us stay at the castle for a while. helped us find our feet.” He paused. “i think... i think he thought we were refugees. or maybe survivors. never pressed us for info, which was nice. he just... let us be.”

Undyne leaned against the wall again, arms crossed loosely. “You two just don’t match anything anyone’s ever seen. Even Gerson said there were no records of skeleton monsters since... what, the old wars?”

Sans let out a low whistle. “yeah. heard that too. guess we’re special.”

“I don’t mean that in a good way.”

He gave a noncommittal shrug. “figured.”

A pause stretched out again, filled only by the distant hum of the lab’s systems. Then Undyne spoke again, quieter this time. “Papyrus always made it sound like you just... stepped in one day. Like you were always there, raising him.”

“kinda feels that way,” Sans admitted. “one moment i’m just a kid, and the next, i’ve got this loud, gangly little brother with zero volume control and infinite enthusiasm. he needed someone. and... guess that someone was me.”

She tilted her head. “And you? Who did you have?”

He was quiet for a beat too long.

“no one, really. i mean—there was asgore. but... you know how he is. always busy. always kind, but a little distant. it was like livin’ in a museum. i got good at keepin’ quiet. keepin’ small.”

Undyne frowned faintly. “That’s not right.”

“nah,” Sans said lightly. “but it’s not wrong either. just... how it went.”

He tapped a few keys and glanced at the screen. “download’s nearly done.”

Undyne didn’t move.

She stood in the soft, sterile glow of the hallway lights, one hand still resting on the haft of her spear, the other hanging loose at her side. But her eye wasn’t on the corridor anymore. It was on him. On Sans, hunched over the flickering console with his ever-slouched posture, his fingers still moving lazily across the keys, as though the conversation they’d just had hadn’t cracked the floor out from under her assumptions.

Things began to settle into place in her mind like puzzle pieces rotated just right for the first time. Pieces that had always been there—oddities and quirks she hadn’t known what to make of. The way Papyrus had stumbled through learning things any kid would have picked up by second grade. How he’d flinched when she’d casually asked, years ago, back in the kitchen during their first proper hangout, if he ever visited his folks. He’d dropped a pepper shaker mid-stir-fry and covered it up with a joke so big and theatrical it practically came with stage lights. She’d brushed it off at the time. Let it go.

But now it made sense. All of it.

All they’d had was each other.

Sans, acting like an exhausted, overprotective single parent half the time, hiding his stress under jokes and slouching sarcasm. Papyrus, clinging to order, pride, rules—anything that gave shape to the unknown. That closeness hadn’t been coincidence or just good sibling chemistry. It had been survival.

Her jaw tightened. She didn’t speak. Just watched.

Sans sat back a little in the chair, cracking a few bones with a lazy stretch of his spine. His eyes drifted up to meet hers and his grin crooked just enough to be familiar.

“you look like you got questions,” he said.

She shifted her weight, rolling her shoulder like the thought had physically brushed past her. “They can wait,” she replied, voice even. “Let’s go fix the generator.”

He chuckled, and the grin broadened. “heh. alright, but you’re not gonna clam up on me later, right?”

She gave him a deadpan stare. “Really?”

“i codn’t help myself.”

Undyne groaned out loud, dragging her hand down her face.

“alright, alright,” Sans said, raising his hands in surrender, still smirking. “guess we’d better scale back the fish puns. wouldn’t wanna flounder in front of the enemy.”

“You’re lucky I like you,” she muttered.

“d’aww.”

He finished the last few keystrokes on the console. The monitor flashed green, pulsing once before a thin arc of light sliced through the air to their left—space folding in on itself with the crisp shimmer of a freshly opened rift. Pale blue and silver, the tear rippled with power, casting a faint glow across the floor tiles and washing both of them in a cool, unnatural light.

Sans stood, brushing nonexistent dust off his hoodie as he turned toward the rift. “after you, captain,” he said, gesturing gallantly.

Undyne stepped forward, spear tight in her grip, her silhouette bold against the glow. She didn’t hesitate. Just looked back at him once—eye steady, brow lifted—and then stepped through the rift with a shimmer.

Sans followed, bones lit in the shimmer of the dimensional fold, giving one last wink at the empty hallway before vanishing into the light.

And when they were gone—

But.

Something remained.

                                          ....Something dark.

Waiting.

Smiling.

Chapter Text

Undyne stepped out of the portal first, boots slamming onto the smooth metallic flooring with a grounded confidence that belied the fatigue she tried to shake off. Her spear was hoisted lazily over one shoulder, the hum of its blade dimming as the rift behind her snapped shut. Sans followed half a second later, hands in his pockets as usual, expression unreadable but casual.

The lab was calmer now—dimmer, almost. The overhead lights still flickered faintly with residual interference, and a low thrum vibrated through the walls like the facility was settling into itself again after years of silence.

Alphys, hunched over one of the large curved monitors, turned at the sound of their arrival. Her eyes widened with visible relief. Undyne shot her a wink and clapped her free hand against her hip.

“Got it fixed,” she said with a crooked grin. “Told you not to worry.”

Alphys made a garbled noise of relief and surprise, her glasses slipping down her snout as she straightened up too quickly. “Y-you did? That’s great! I was just—uh—monitoring the—uh—stability readings. They were, um, fluctuating a bit, but now that you're back—um—thank you!”

Undyne waved a hand dismissively. “Nothing we couldn’t handle.”

Sans didn’t pause to add to the exchange. His steps carried him across the lab to where his brother stood near one of the central consoles. Papyrus’ shoulders were tense, his posture unusually subdued as he listened to Frisk, who was signing something with deliberate motions. Their hands moved with care, pausing here and there for emphasis, and their eyes were gentle, focused entirely on Papyrus.

It was Frisk who noticed Sans first. They turned at the soft sound of footsteps and immediately perked up, their face lighting with something between relief and curiosity.

“How’d it go?” they asked aloud, hands briefly lifted but not signing this time, waiting for a verbal response.

Sans gave his signature half-grin, the corner of his mouth tugging upward like a reflex. “easy peasy,” he said, dusting off his hoodie with exaggerated effort. “like takin’ a nap on the job.”

Behind him, he could feel Undyne’s glare on the back of his skull like a sunbeam cutting through ice. He didn't acknowledge it.

Alphys, meanwhile, had adjusted her glasses and turned back to the monitor, scanning the data with a furrowed brow. “Looks like everything’s stabilised,” she muttered. “The primary systems are all back online, and there’s no sign of increased decay in the core infrastructure.” She paused, clicking something. “Though, there was a spike in activity while you were both down in the labs.”

Sans raised a brow. “yeah?”

“Yeah.” Alphys tilted her head, looking over her shoulder at him and Undyne in turn. “Did you notice anything unusual? A shift in the magnetic field? Sudden anomalies? Increased radiation signatures?”

For a moment, the air hung thick.

Undyne sighed. Her arms were crossed, weight shifted to one side, spear now clipped against her back. “Sans saw something.”

That drew a flicker of expression from Papyrus. His browbone dipped slightly, his sockets narrowing in concern, but he didn’t speak.

Alphys blinked. “Something? What kind of something?”

Sans scratched his skull. “not sure,” he said, tone even. “guess i forgot.”

Alphys stared.

Papyrus did too, his gaze lingering now on Sans with something unreadable behind his expression—something searching. Something questioning. But he didn’t say anything.

Alphys’ eyes bounced between the two skeletons, the silence stretching just long enough to be uncomfortable before she cleared her throat and turned back to the data streams. “Well… everything looks fine now. All systems are nominal. Once we finish sweeping the remaining files and checking for residual fluctuations, we should be able to head back topside.”

She clicked a few keys. “Report back to Asgore, let him know the lab’s stable. Shouldn’t be more than a few hours.”

“great,” Sans said, rocking back slightly on his heels.

Undyne exhaled, shoulders relaxing now that the pressure of their mission had—temporarily at least—lifted. She looked over at Frisk, who’d moved closer to Papyrus again, their gaze still locked on Sans.

They were signing.

'You really forgot?' their hands moved gently, cautiously. 'Or you don’t want to say?'

Sans watched their fingers. For a beat, he didn’t answer. Then he shrugged.

“bit’a both, maybe.”

Frisk’s mouth pressed into a thin line, and they dropped their hands to their sides.

“hm.”

Papyrus shifted, his gloved fingers curling slightly where they rested at his side. “Well,” he said at last, “I’m glad everyone’s safe. That’s what matters most. Good work, everyone!”

His voice was too bright, a bit too stiff. He clapped his hands together once with theatrical cheer and gave Frisk an encouraging pat on the back.

Frisk smiled faintly but didn’t look away from Sans.

Sans just smiled back.

Undyne rolled her neck, cracking it loudly. “We should rest a bit before going back in,” she said. “Refuel. Alphys, you got any of those dehydrated noodles left?”

“Uh—y-yeah, check the drawer by the fridge,” Alphys replied, still clicking through data. “And there’s bottled water in the cooler. I’d stay away from the canned spaghetti though—uh, it expired… two years ago.”

Papyrus gasped.

“What?! SACRILEGE!”

Undyne barked a laugh. “Don’t worry, Paps, we’ll survive.”

As the others moved to settle in—some stretching, others rummaging for food—Sans lingered by the far terminal. He stared at the glowing lines of code scrolling slowly down the screen, unreadable even to him. His sockets narrowed slightly.

There was a flicker—barely perceptible, a flash too fast for conscious thought. Just a stutter in the screen’s refresh rate. A line of something that didn’t belong.

He blinked. It was gone.

He didn't mention it.

He turned and walked over to join the others, whistling low under his breath.

He kept it casual—hands in his pockets, steps slow, shoulders relaxed—but the tune he whistled didn’t have a melody. It wasn’t a song, not really. Just notes picked at random. No rhythm. No pattern.

His mind was elsewhere.

He thought about what happened in the True Labs. Or—what he thought happened. That was the problem, wasn’t it? He saw something. He swore he did. A shape, a flicker, a ripple in the air like heatwaves distorting the edge of his vision. Something too quiet and too still to belong in a place that was already filled with ghosts of broken science.

But the memory kept sliding out of his grasp.

Like trying to hold water in a sieve.

He rubbed the back of his neck absently, sockets narrowing. Papyrus had the same issue a little while back. He’d asked—lighthearted, offhand, the way he always did when he was testing something out in private.

Papyrus had just frowned. Said he remembered walking, and talking, and looking, but not much else.

“It was like waking up and knowing you dreamed,” he’d said. “But the dream’s already gone.”

No one else seemed to be affected. Not Alphys. Not Undyne. Not Frisk.

Just him.

And Papyrus.

His mind drifted back to the tremors. The ones that rattled the bones in his feet and made the lights flicker in rhythm like a pulse. They’d seemed strongest near the Core—near what was left of the Core. That place had always been a mess of unstable energy, cracked dimensions and timelines held together with duct tape and stubbornness, but this felt… different.

Less chaotic.

More deliberate.

He glanced back toward the others. Frisk was showing Alphys something on the monitor, signing one-handed while munching on a nutrient bar with the other. Papyrus had seated himself beside them and was listening intently, his expression open and curious, asking questions between every sign, clearly trying to follow along. Undyne had taken up a spot by the cooler, arms folded, sipping from a bottle of water like it was a beer at a victory party.

They looked fine.

Normal.

He shuffled out of the room quietly, the sound of his footsteps swallowed by the hum of distant machines. The hallway that extended deeper into Alphys’ lab yawned before him like the throat of something ancient, long-abandoned and still hungry.

His skull tilted as he walked, step after step echoing down the metallic corridor. Pipes lined the ceiling above, some hissing softly with steam. The walls were painted a sickly greenish-grey, cracked in places where the structural integrity of the underground had taken its toll.

Things weren’t adding up.

And it was annoying him.

He hated not knowing things.

Especially when the missing pieces were lodged somewhere inside his own head.

He turned a corner, passed the old data server room—long since disconnected—and headed further down. The light grew dimmer the deeper he went, flickering lazily, like the building itself didn’t have the energy to keep the lights on in places no one was supposed to go anymore. The quiet here wasn’t like the quiet above. It didn’t feel like a pause. It felt like an inhale that never let go.

He passed a couple of rooms without realising. Doors with blank or half-scraped nameplates, walls warped slightly with age and pressure. It was only when his left shoulder brushed against the doorframe of a room and he paused to glance inside that he blinked and took in where he was.

A filing room.

Not particularly large, but dense with content. Cabinets lined the walls from floor to ceiling, stuffed with manila folders and curled sheets, some sealed and stamped, others barely held together with ageing paperclips. A desk sat to one side, unoccupied but layered in stacks that looked like they’d been shuffled through repeatedly by someone looking for something very specific—or perhaps forgetting what they were looking for halfway through. A portable light sat dark in the corner, the bulb long dead, its cord coiled like a sleeping snake.

Sans frowned slightly, his sockets narrowing.

“huh,” he muttered to himself, scratching just above his brow ridge. “don’t remember makin’ a pit stop here.”

His feet had taken him here all on their own. Not that it was unusual—his sense of direction often worked on instinct more than intention—but still. Of all the rooms he could’ve wandered into, this one? It didn’t feel random.

“welp.”

He gave a shrug like it didn’t matter, pulling his hands from his pockets and dusting one off against his jacket. A quick glance around confirmed there wasn’t much in the way of recent activity—no fresh footprints, no tools or notes left mid-use, no coffee cups or Alphys’ usual trail of snack wrappers. The air smelled like paper and old glue, faintly metallic, as if even the dust here was archival.

He ambled toward the nearest cabinet, scanning the faded labels haphazardly scratched into the metal. Most of the filing drawers had alphabetical tags, though the organisation was more theoretical than practical. Some drawers were jammed too full to close, while others hung open at odd angles, their contents spilling slightly like dislocated bones.

“let’s see what kinda bedtime stories we got in here.”

His finger drifted lazily along the drawer fronts.

A – Amalgamate
B – Baseline Readings
C – Core Diagnostics
D – Determination Trials
E – Experiments, Failed
F – Fallen Down
G – Gast-

Static.

Suddenly and violently, his vision filled with it.

A burst of harsh, white noise surged through his skull like a spike driven through the base of his spine. Every light in the room surged brighter, popped, then flickered off entirely. His sockets flared wide, and his body jerked backward with enough force that he slammed into the edge of the desk behind him, scattering papers to the floor.

For a moment, he was somewhere else.

Or maybe he wasn’t anywhere at all.

The sensation wasn’t like teleportation. It was disorienting, gut-deep wrong in a way that turned his soul sideways. His balance reeled. He was aware of something just out of sight—no shape, no colour, just a pressure behind his sockets like a hand pressing through fog, almost touching bone.

He blinked rapidly, breathing sharp through gritted teeth, the bones in his fingers twitching with residual static. His vision swam with afterimages: jagged lines, overlapping shapes, words he didn’t understand. The fluorescent lights buzzed back on a second later with a harsh click, returning the room to its usual dreary pallor.

But the feeling hadn’t gone.

He pushed off the desk slowly, one hand braced against the edge, the other rising to rub between his sockets. The motion was mechanical, more like he was checking to make sure his skull hadn’t cracked in half than anything else.

“that’s new,” he muttered hoarsely, trying to force levity into his tone.

It didn’t quite land.

His gaze darted back to the drawer labelled ‘G’, which now hung slightly open. It hadn’t been open before. He was sure of that. He stepped forward cautiously and stared at it, waiting for the flicker, for the sharp pain to return—but nothing came. Just that creeping feeling under his ribs. That pressure. Something watching.

Very carefully, he reached out and slid the drawer open further.

It moved smoothly.

Inside, the files were stacked neatly.

Too neatly.

Each one aligned with unsettling precision, as if placed by a machine or a hand that understood obsession better than organisation. No casual thumbprints, no corners folded from repeated reading. Just pristine, dustless order. That was wrong—this place hadn’t been touched in years, maybe longer. But these folders were as fresh as yesterday. Like they were waiting for him.

Sans let his fingers hover a moment before they brushed lightly over the contents, fingertips drifting over typed labels and inked codes, pausing now and then as his sockets darted across unfamiliar names, strange acronyms, phrases that stirred something in the darker recesses of his memory. Files labelled with things like “Anomalous Behaviour: Core Convergence”, “Temporal Phase Displacement”, “Echo Log Inconsistencies”. Others had only numbers—no titles, no identifiers, just strings of digits that meant nothing on their own but felt somehow heavy, like the bones of old secrets.

His fingers froze on a thick manila folder, heavier than the others. Its tab had smudged handwriting barely legible beneath layers of old pencil markings and faded pen.

“ga—” he whispered, squinting. “gust…?”

His voice dropped off. That wasn’t right.

The rest of the name had been scrubbed out. Not erased—removed. Like someone had gone at it with time itself instead of ink.

His gut clenched, and he slowly pulled the folder free, his thumbs pressing into the cover like it might bite back. The edges were worn, and when he cracked it open, a musty scent wafted up from within—a cocktail of old paper, chemicals, and something deeper. Something sterile. Surgical.

A single page slipped free the moment he opened it, tumbling downward like it was trying to escape. Instinctively, his magic flared.

He caught it in the air, golden light flickering faintly at the edges of the sheet as it hovered just before his eye level. The words on it were scrawled in heavy, urgent handwriting, with corrections messily scratched in the margins.

He read it once.

Then again.

Each time slower.

“Subject 1 has woken up.”

There was no name. No context. No date. But he didn’t need any of that.

Because in the space between the words, in the pause his soul made when it processed them, everything inside him remembered.

It didn’t come as a clear memory. It came as flashes, gut-churn jolts of sensation that ripped through his mind like claws dragged through water—broken reflections, distorted noise, too fast to catch.

White lights above an operating table, flickering like a heartbeat.

The scream of drills in metal and bone.

Crying. Not his. Someone small. Someone nearby.

A hammer hitting something hard. A sound like marrow cracking.

A voice—no, two, layered over each other, one familiar, one guttural—saying something over and over but getting cut off by static.

And then a BOOM. Bone shattering. Magic, thick and hot. A hand reaching out. A door slamming shut.

His breath caught in his throat. His magic pulsed outward uncontrolled—like a wave—and before he realised what he was doing, the folder launched itself out of his hands. It hit the wall with a solid crack, then burst open as its contents scattered across the floor like thrown shrapnel, papers fluttering in every direction.

Pages. Photos. Diagrams. Sketches. Some looked like anatomical studies. Others were blurred beyond comprehension. One had a hole burned straight through the middle, like something had tried to erase it from both sides.

He staggered backward a step, bracing himself against a nearby cabinet. His breath was shaky, harsh, pulled through gritted teeth. The back of his jacket was damp with cold sweat. His skull throbbed.

He squeezed his sockets shut and tried to blink the fog away.

It clung to him.

A phantom ringing filled his earhole—high-pitched, insistent. Not sound exactly, more like pressure given voice. The kind of noise you didn’t hear but felt in the gaps between thoughts.

He opened one eye.

The paper he’d caught earlier—“Subject 1 has woken up.”—lay at his feet, edges curling. Its ink was running now. Bleeding outward, like whatever was written didn’t want to be read again.

But suddenly he had the sinking feeling that he’d already started to.

Another tremor shook the floor—brief, light, but just enough to unsettle the cabinets around him. They creaked like a breath being held. A couple loose sheets slid closer toward the centre of the room, drawn inward like tide to a drain.

“okay,” he whispered to himself, still kneeling, his voice dry and thin. “okay.”

He stayed like that for a breath longer, spine hunched, sockets half-lidded, letting the air settle back into silence—until it didn’t.

Footsteps.

Rhythmic, purposeful.

Not loud. Not hurried. Just present. Coming closer.

He straightened up fast, spine stiffening as the noise crept nearer down the hall. The click of boots. The scuff of claws. Fabric brushing against door frames. He had enough time to swallow, to brush a few creases from his jacket, and wipe the cold sweat from his skull with one shaky sleeve before the door opened.

The light from the corridor spilled in, harsh and uninvited, splashing across the paper-strewn floor like a spotlight on a crime scene.

Alphys stepped in first, hugging a tablet against her chest. Her lab coat flapped slightly as she halted just past the threshold. Her eyes went wide when they landed on the cabinet—still ajar, still visibly scorched. Then her gaze flicked to Sans.

Undyne followed close behind, one brow cocked. She let the door swing wider as she stepped in, arms folded, expression caught somewhere between concern and readiness to fight something. Anything. Even a filing cabinet.

Frisk slipped in after them, quiet. Observant. They stayed near the door, head tilting slightly to one side as their eyes scanned the room with practiced calm. They didn’t say anything.

Papyrus brought up the rear, tall as ever and trying to peer over everyone's shoulders. He ducked slightly to get a better view, his posture already tensing with worry.

No one said anything at first. The hum of the old ventilation system filled the silence like a poor substitute for words.

Then Alphys spoke, voice thin with unease.

“…what happened in here?”

Sans didn’t answer.

Not at first. He turned back toward the folder—now halfway across the room where his magic had flung it—and began to take a slow step, but Undyne moved quicker.

She strode forward and scooped up the folder before he could reach it. Flipping it open, she scanned the top page, her single eye narrowing as she tried to make sense of it.

“What even is this?” she muttered, holding it closer. “Looks like symbols. Kinda like… a tear drop? No—wait—a diamond. And this one’s like a scorpion tail. Like that weird ‘M’ thing.”

“Scorpio,” Alphys corrected automatically, stepping closer. “That’s the symbol for Scorpio.”

Undyne rolled her eye. “Yeah, that. What’s it mean?”

“I… I don’t know,” Alphys said. She leaned in to peer at the symbols herself, shoulders twitching as she adjusted her glasses. “I mean, I’ve seen weird codes before—hell, even made some myself—but this? This isn’t standard lab encryption. This doesn’t even look like a language. It’s—”

“It's too clean,” Sans muttered.

They all turned toward him.

Frisk, still silent, crouched near a cluster of loose pages and started carefully gathering them. Their eyes lingered on one in particular—covered corner to corner in densely packed glyphs. Lines and arcs and fragmented shapes. They tilted their head again. Then held the page up, angling it toward the light.

Alphys stepped forward to get a better look, but Papyrus beat her to it, his gaze sharper than usual.

“Wait,” he said, his voice quiet.

Everyone paused.

He stared at the page in Frisk’s hands.

Then his gaze drifted to the open folder in Undyne’s grip.

Then to the wall where the three vertical marks were still faintly visible.

“I… I think it’s Wing Dings.”

A beat.

Undyne frowned. “Wing what now?”

Papyrus blinked. “It’s—um—it’s a font. Or. A cipher? I mean—it’s not technically a language but—” He hesitated, glancing at the others as if he was hearing his own words for the first time. “I don’t know how I know that. I just—do. I looked at it and I knew.”

Frisk stood slowly, their eyes fixed on him. They didn’t say anything—just offered the page over with both hands.

Papyrus took it with a careful reverence. The symbols sprawled across it pulsed faintly in the overhead light. Black ink, heavy on the page, some of it smudged but still coherent in a way that made Sans’ magic itch behind his sockets.

Papyrus’s fingers traced one line, then another.

Then he spoke.

Softly.

“It says… ‘phase instability nearing threshold. Sub-1 remains lucid.’”

“What the hell does that mean?” Undyne asked, stepping in closer.

“‘Sub-1’…” Alphys echoed, murmuring under her breath, eyes scanning the page in Papyrus’ grip.

Frisk signed something.

“The tremors started weeks ago.”

Then, after a moment, they added aloud, “We weren’t down here yet.”

Alphys blinked. “You’re right. They started before any of us accessed the lower levels again. Even the True Lab was locked up until today.”

Sans kept his gaze on the mark scorched into the far wall. He didn’t move, didn’t speak. His hand twitched slightly at his side.

Papyrus was staring at him now.

“…Sans,” he said slowly. “Do you understand this?”

Sans’ jaw clicked faintly as he gritted his teeth.

“I dunno,” he muttered.

It was a lie. Not a full one. But close enough.

He shouldn’t understand it. He shouldn’t feel anything at the sight of those symbols. But deep down, something in him was moving. Turning gears that had been rusted over. Old instincts. Like his magic was remembering something his mind wasn’t ready to catch up with.

Frisk stepped closer to him. Close enough that he had to look down slightly to meet their gaze. Their eyes were steady, unreadable.

They reached for his hand. He didn’t pull away.

“Something’s been buried here,” they said quietly. 

Sans didn’t speak.

Frisk continued, tone flat but steady. “You saw something. Didn’t you? Before we came in.”

He nodded once, slow and small.

Papyrus glanced between them. “Saw what?”

Sans finally looked at him.

“Memories,” he said. “Or… not quite. Fragments. Flashes. Can’t pin 'em down. Like trying to grab fog.”

Alphys was staring at the page again, the edge trembling slightly in her grip.

Undyne’s voice was rough. “Someone did this. This whole thing—this code, this drawer—it’s not random.”

Alphys nodded. “It was meant to be found.”

The light overhead flickered again. Dust stirred in the corners.

Papyrus frowned. “But if it’s Wing Dings… who wrote it?”

The room fell quiet.

A beat passed.

Then another.

And Frisk, eyes narrowed and tone cold, asked softly:

“…Who was Subject 1?”

Chapter Text

Chapter Text

The silence inside the small, dilapidated room carried a weight of its own. Between the soft hum of ancient, broken-down electronics and the faint hiss of failing overhead lights, there was nothing but the sound of heavy breathing and the low, distant groan of the facility around them—like the whole Underground was holding its breath.

Everyone’s eyes had turned to the pair of skeletons.

Sans still hadn’t moved from where he stood, head low and spine curved forward, as though gravity had grown heavier just for him. Papyrus hadn’t let go yet, still holding his brother like he could somehow shield him from whatever memory or nightmare had returned. For a moment, it was like nothing else in the world existed for them but each other—Frisk, Undyne, Alphys, all standing still at the edges of something too quiet to interrupt.

Frisk watched closely.

They weren’t sure what passed between the two skeletons, but it was clear something did. Papyrus shifted back just slightly, his orange eyes searching his brother’s face with open worry. His mouth was tight, drawn into a firm line of anxious determination. Sans didn’t meet his gaze directly—his own expression was distant, almost hollow, like he was somewhere else entirely. But he wasn’t blocking his brother out. There was a quiet exchange there, one that didn’t need words.

Papyrus tilted his head, silently offering something unspoken.

Sans breathed out through his nose and gave the barest shake of his head.

Even without speaking, they said volumes.

Undyne stepped forward, cutting through the stillness. Her voice was softer than usual—measured, not forceful, and tinged with a mix of concern and grit.

“You know him… don’t you.”

It wasn’t a demand. It wasn’t even suspicion. It was a statement. Weighted.

Papyrus let go of his brother then, hands slipping from his shoulders slowly, like he was reluctant to remove the contact. Sans’s body tensed slightly at the loss of it. His hands twitched by his sides. When he didn’t speak, Papyrus cleared his throat, casting a glance at the others before looking down.

“We… have history,” he said carefully.

The words hung in the air, too vague to be comforting.

Undyne’s expression hardened slightly with restrained confusion. “What kind of history?” she asked. “Why didn’t you tell us? How long have you—?”

She didn’t get to finish. Alphys, who had been quiet up until now, stepped in quickly, moving to stand between the brothers and Undyne with a subtle shake of her head. Her voice was soft but firm, the way someone speaks when they’re trying not to startle a wild animal.

“They don’t… they don’t have to talk about it,” she said. “Not if they’re not ready.”

Frisk nodded slowly, standing beside Alphys. Their fingers shifted, hesitant, before signing gently: “You don’t have to, but we’re here if you want to.”

Sans's shoulders rose in a silent breath, and then he finally moved. His gaze lifted, meeting no one’s eyes directly. His voice was quiet, gravelly with a tiredness that didn’t come from exhaustion but something deeper—older.

“He made us.”

Alphys blinked.

“…What?” Undyne’s voice cracked on the word, not out of disbelief, but confusion.

Frisk looked up at Sans, eyes wide.

He swallowed hard, like the words were knives in his throat. “Gaster,” he said, more firmly. “He didn’t just know us. He… he created us.”

The words dropped like a stone into the room.

Alphys stared, breath caught in her throat.

Papyrus shifted awkwardly, looking down again as if ashamed.

Sans rubbed at the back of his skull, glancing at the floor as he went on, his voice shaking with a strange bitterness. “We’re not… like other monsters. We weren’t born. We weren’t found. We were made. Everythin’s just… it’s coming back. The stuff we forgot. Or were made to forget.”

Undyne looked between them, disbelief creasing her brow, though it was slowly eroding into something else. “What do you mean, made?” she asked. “Like… magic cloning or something?”

Sans barked out a laugh, sharp and humorless. “Nah. Worse.”

Papyrus reached out, lightly grasping his brother’s arm in silent support.

Sans didn’t pull away this time. He closed his eye sockets for a long moment before continuing.

“He didn’t just use magic. He used part of himself. His soul. Pieces of it. Split it, carved it up to make us. That’s why he called us thieves—’cause we are. Whether we wanted to be or not.”

Alphys’s hands went to her mouth, and she staggered back half a step.

Undyne blinked, stunned into stillness. “You’re saying… you’re part of him?”

“No,” Papyrus said gently. “We were made from him. Not part of him. It’s different. It has to be.”

“Subject One,” Sans said bitterly, eyes narrowed. “That was me. And Paps was Subject Two. Guess we didn’t have names ‘til later.”

Frisk reached out, unsure, signing: “You didn’t remember this until now?”

“Nah,” Sans muttered. “I remembered bits. Always wondered why we didn’t… y’know. Have a past. A family. Records. Just popped into Snowdin one day. Acted like we’d always been there. Everyone just… accepted it.”

Papyrus nodded, slowly. “It’s like… dreams,” he said. “Or static. I’d remember a laugh that didn’t belong to me. A room that never existed. But every time I tried to think about it too hard—gone.”

Alphys turned toward them slowly, mouth still partly open. “Gaster’s research,” she whispered. “It was… it was about soul fragmentation. Weaponisation. I saw notes once—I thought it was theoretical. Or that it failed.”

“It should’ve failed,” Sans said quietly. “We weren’t supposed to live. We weren’t supposed to remember either. Guess he messed up twice.”

Silence settled again, this time different. Not just shock—but the uncomfortable weight of reality sliding into place.

Frisk moved to stand beside Sans fully now, lifting their hands.

“You’re not him. You’re not what he wanted you to be.”

Sans looked down at them slowly.

Papyrus smiled, just barely.

Undyne stepped forward, voice lower now, not questioning—more like grounding. “What does he want now? Why come back now?”

Sans shook his head. “Dunno,” he said. “But he looked at me like we stole somethin’.”

Papyrus’s brow furrowed. “I'm not a thief...”

There was a long pause.

Undyne crossed her arms, still visibly shaken, but now sharpening with a renewed sense of purpose. “Doesn’t matter what he made you for,” she said, voice low and resolute. “You’re our friends. You chose who you wanted to be.”

“Damn r-right,” Alphys added, a little shakily.

Frisk signed again, then said softly, “We’re with you.”

Sans looked at them, and for the first time since Gaster appeared, his expression softened.

Just a little.

The brothers look around slowly.

Papyrus takes the lead at first, his tall frame rigid as his eyes scan the decayed hallway. Everything around them is dusted in ash and faded age—broken wires loop from the ceiling like vines, walls peeling like old bark, shadows clinging to the corners like memories that didn’t want to let go.

He lifts his hand and touches the wall as they move forward, his fingertips brushing against a cracked section of concrete like it might spark something clearer, something deeper. It almost does—his face flickers with a half-formed expression of recognition. But what shows more than anything is pain.

“We… were raised here,” Papyrus says finally, his voice gentle and strained. “Sans and I… this was our home. Once.”

The words drop into the silence like stones dropped into deep water—slow and heavy.

Alphys flinches a little, even though she was expecting something like this. Frisk steps closer behind her, their hands half-raised with signs, unsure whether to speak or wait. They’re watching Papyrus carefully.

Papyrus lifts a hand again and gestures to the corridor ahead. “Down the hallway was our room,” he says, voice quieter now, like he’s speaking to ghosts. “To the right, that was Gaster’s office. And further down was…”

He trails off.

The pause tightens like a noose.

His mouth moves but no sound follows. His hand hovers, frozen halfway to pointing.

It’s Sans who speaks next, low and blunt, almost flat, but with that same edge of tension in his shoulders that never truly went away since Gaster appeared.

“Experiments,” he finishes simply.

No one breathes for a moment.

Alphys covers her mouth, visibly paling. Her glasses tilt forward as she lowers her head, her eyes wide and unblinking behind the lenses. Even Undyne seems off-balance, her arms folded tightly across her chest now—not defensive, but protective, like she’s trying to keep the chill from seeping in.

Frisk doesn’t look away. Their hands move carefully.
“You remember all of it now?”

Papyrus doesn’t answer. His posture says enough. He’s shaking, just a little. Whether from cold or memory is impossible to tell.

Sans finally looks up, slowly, eyes sweeping across Alphys, then Undyne, then Frisk. His voice is low. Hollow, but certain.

“Me ‘n Papyrus,” he says, “we’re part of Gaster’s soul.”

Even now, even after everything they’d heard so far, that silences the room like a lock turning. A slow tension rises.

Alphys stares. Undyne mutters, “What—?”

Sans presses on, tone dry and even. “Not like... metaphorical or anything. Literal. He splintered his soul, carved it up. Used pieces to form us. That’s why we can use his magic. That’s why... why we’ve always been a little different.”

Papyrus swallows and takes a careful step forward, standing beside his brother like a memory made flesh.

“Gaster wanted to break the barrier,” he says softly. “But not the way everyone thought. Not with patience or mercy. He didn’t believe in balance. He believed in force.”

“And he needed power,” Sans adds.

Frisk’s hands move slowly, hesitantly.
“From human souls?”

“Yeah,” Sans mutters. “Six human souls. Same as Asgore collected. But instead of storing them in containers, he tried... transfusion. Integration. Infusion.”

Papyrus closes his eyes. “He put them in us.”

The air in the hallway grows cold.

Papyrus lowers his head, as if ashamed. “I’m half bravery,” he says, his voice so soft it barely echoes, “and half kindness.”

Frisk’s expression flickers in subtle surprise.

“And I’m half justice,” Sans says. “And half integrity.”

The words echo. The silence afterward is louder.

Undyne doesn’t move right away. Her face is unreadable at first—then slowly sharpens, jaw tensing, arms still folded. She glances between them, her voice low and steady when she finally speaks.

“Did… Asgore know?”

“No,” both brothers say in unison.

Sans doesn’t elaborate, but Papyrus adds, “Wing Dings didn’t share. Not with anyone. He worked alone. Obsessively. He said even the King wouldn’t understand.”

Alphys shakes her head. “There were rumors. Whispers. But I never—I never imagined—”

“Yeah,” Sans says, voice dry. “Nobody did. That’s the point.”

Frisk lowers their hands, watching both brothers closely now. Their fingers twitch slightly, but they don’t sign anything this time. There’s too much weight in the air.

Undyne finally steps closer, her voice more strained. “Are you saying you’ve got... human soul traits inside you? Like, permanently?”

“Pretty much,” Sans replies. “Not... whole souls. Not exactly. But fragments. Enough that it’s in our magic. In how we were made. It’s part of why we survived. Why we’re... strong.”

“Why we’re stable,” Papyrus corrects gently.

Sans huffs. “That’s a generous word, bro.”

“You’re saying Gaster did this to you,” Undyne says, her voice now strained, anger seeping through the corners of her tone. “Used human souls—experimented on you—and no one ever stopped him?”

“Who would’ve?” Sans snaps, sharp for the first time. “No one even remembered him once he fell. Nobody knew we existed.”

“Everyone forgot,” Papyrus whispers. “Even us.”

The group falls quiet again.

The weight of that room bears down on them. Walls that once held children now only echo with the ghosts of screams and static.

Frisk lifts their hands again.

“You’re not him. You didn’t choose this.”

Papyrus looks at them and smiles, sad but soft. “No. But we choose who we are now.”

“And who we protect,” Sans adds.

They stand there a while, not moving. Letting the weight settle. Letting truth hang in the air like dust that had never settled until now.

Then slowly, quietly, Papyrus turns toward the hallway. “The room’s still down there,” he says. “If it’s still intact.”

Frisk signs:
“We’ll go with you.”

Sans nods once, and the others follow.

The corridor stretches ahead like the throat of some long-dead machine. It swallows the light behind them, every step echoing with a low, hollow rhythm that makes the walls feel closer than they are. The concrete underfoot is stained with time—grey on grey, old watermarks like faded blood pooled in corners. There’s a weight to the air here. Thick. Damp. Like even the air remembers what happened within these walls.

The brothers take the lead.

They walk side by side, but it’s clear they’re each inside their own head. Papyrus’s steps are light, too light, like he’s trying not to touch the ground. His hand hovers near his side, not swinging freely like usual. Sans, by contrast, is silent in a different way. Shoulders hunched, head low, his gaze flicks over every crack in the wall like he’s scanning for ghosts—or traps.

Behind them, the others hold back. It isn’t cowardice, just hesitance. A shared understanding that this stretch of hallway doesn’t belong to them, not really. This place was once a home for two, and everything ahead is layered with memories that no one else can touch. Not properly.

Frisk lingers between Alphys and Undyne, walking in measured steps. Their fingers flex in and out of sign, half-starting a phrase only to let it drop. There’s nothing they can say yet that feels right. Alphys seems shaken again, her eyes wide behind her fogged glasses, arms tight against her chest like she’s bracing for an explosion. Undyne is more overt—tense jaw, fists clenched, her eye twitching from left to right like she’s daring something to come out of the shadows so she can beat the hell out of it.

When they reach the door—the one that even the walls seem to lean away from—Papyrus gives it a wide berth.

Not subtly, either. He visibly swerves as they draw closer, the movement clumsy, almost too large. He doesn’t look at it. Not even out of the corner of his eye. Like if he doesn’t see it, it can’t see him either.

Sans glares at the door.

It’s the kind of look that doesn’t just simmer—it burns. His usually slack expression tightens, lip twitching once at the corner like he’s chewing something sour. But he doesn’t stop. He doesn’t even glance toward the others. Undyne notices. Her eye narrows, matching the tension in her shoulders. No words are exchanged, but the message is loud and clear.

She’s ready. He is too.

Behind them, Frisk slows, glancing between Papyrus and the door. Their hand lifts slowly, fingers shaping a simple word:
“Okay?”

Alphys sees it too and touches their wrist gently, her face pale but steady. “I think they need to go at their own pace,” she whispers.

A few more paces down, the brothers stop. This door is different. It doesn’t hum like the experiment room. It’s quiet. Just another dull, metal slab in a hallway of the same. But Sans stares at it for a moment longer, then turns to his brother.

He smiles.

It’s small. Careful. But genuine.

“You don’t gotta look,” he says softly.

Papyrus straightens.

There’s a beat of silence. Then:

“I’m not called The Great Papyrus for nothing!” he declares with a flicker of old pride. His voice is steadier now, even if it’s a little forced. “A little door won’t stop me!”

And he reaches for the handle.

The door creaks open with a dry wheeze.

They step inside.

Everything stops.

The room isn’t large, but it feels cavernous. Like the walls have receded from the years of silence and disuse. The air is stale, sealed in for what feels like centuries. It carries the sterile tang of long-dried antiseptic and the faint scent of dust-covered metal.

On opposite walls, two metal shelves hang crookedly—one partially collapsed under the weight of old rust. Between them, the floor is empty save for a green hospital gown, crumpled in a loose heap like whoever had worn it had simply evaporated.

Papyrus gasps, soft and sharp. It’s not dramatic. It’s not even that loud. But it cuts through the quiet like a blade. He steps inside fully, sandals brushing against the tile as he kneels beside the gown.

Sans hangs back, leaning in the doorway, his eyes locked onto his brother’s every move.

Papyrus doesn't reach for the gown. Instead, he runs his hand across the floor nearby, fingers dipping into a narrow gap behind one of the shelves. When he stands, there’s something small and colourful in his hand.

A Rubik’s Cube.

The colours are faded—some of the stickers are peeling—but it still turns, clicking softly as he rotates it in his hands with a flick of familiarity.

“I thought I lost this,” he says quietly, wonder bleeding into his voice. “But I must have left it here… when we.”

The silence that follows is strange. Heavy, but not sharp. The others don’t know what to say.

Undyne shifts awkwardly before glancing at Sans.

He meets her gaze, then gives a small nod toward his brother.

She steps forward.

“Yo,” she says, her voice pitched a little softer than usual. “That thing’s one of those puzzle cubes, right? Never could figure those out.”

Papyrus perks up slightly, the tension in his shoulders easing.

“It was a gift!” he says brightly. “From Dr. Gaster! He said it was a symbol of layered complexity and unresolvable paradoxes—though he also called it a ‘distraction cube’ when I played with it too much during sessions.”

Undyne chuckles. “Bet you got real good at it, huh?”

“Of course!” Papyrus says, a hint of pride returning. “I could solve it in forty-eight seconds! My personal best!”

He starts to ramble about different algorithms he used to practice, about how he used to assign letters to each colour so he could remember the rotations in patterns, and Undyne smiles, nodding along, letting him talk.

Behind them, Sans walks over to Frisk and Alphys.

Alphys looks up, her expression drawn tight. “Sans—”

“Don’t,” Sans says sharply, voice low and dangerous now, a far cry from his usual casual tone.

They both freeze, looking at him.

“I’m not,” he continues, “letting Gaster anywhere near my brother ever again.”

Frisk signs, slowly,
“He’s safe now. We’re all here.”

Sans glances at them, then nods once, a stiff motion.

“I know,” he says. “But just being back here... I can feel him. Like he’s still in the walls. Watching. Waiting.”

Alphys’s hand trembles slightly at her side.

“I—I didn’t know,” she says.

Frisk frowns, their eyes lingering on Papyrus, who’s now showing Undyne how to rotate one side of the cube. There’s something lighter in his posture—just barely—but it’s enough to show he needed that. Something familiar. Something his.

“He’s stronger than he looks,” Frisk says aloud, voice soft, their fingers still loosely signing. “You both are.”

“Yeah,” Sans says. “But strong doesn’t mean we’re unbreakable.”

The shadows feel thicker in this room, like the space is remembering what it used to be. But now, there’s light here too. There’s a group of people who made it this far, who know the truth, who stayed even after knowing.

And that matters.

Papyrus laughs suddenly, not loudly, but enough that it rings in the room. Undyne fumbles the cube and it clatters to the ground. Papyrus stoops to pick it up again.

“See? Easy!” he grins. “All in the wrist!”

Sans watches him, eyes softening at the corners.

Alphys glances at Sans. “What now?” she asks quietly.

He doesn’t answer at first. Then he looks down the hallway, toward the experiment room. Toward the past.

sans’ eyes narrow, sockets dimming beneath the brim of his hood. His voice, when it comes, is low and weighty.
“in that room,” he says, glancing sharply to the sterile door down the hallway, “there’ll be logs. files. stuff on gaster—stuff he didn’t want anyone else knowing. probably hid it even from himself.”

He doesn’t point. He doesn’t have to. The air around the corridor is already dense, thick with dust and memory, and the others know exactly which room he means. The one that’s still locked. The one no one’s gone near. The one Gaster once called Observation.

Frisk, standing beside Alphys, shifts on their feet. They look up at him—sharp, attentive eyes flicking between Sans and the hallway. A silent question curls in their throat, but it doesn’t need to be spoken aloud. Sans reads it anyway.

“i’d go with you,” he says, then looks back toward where his brother stands with Undyne, who’s trying to distract him with a story about a time she’d fought off three knights with nothing but a soup spoon. Papyrus is listening, but his eyes keep trailing back to the rubik’s cube in his hands. The one he found. The one Gaster gave him. His long fingers twist it almost without thought.

Sans doesn’t finish the sentence. Doesn’t need to. The hesitation says it all.

Frisk nods slowly. Then signs, “We understand.”

He offers them a tired smile that doesn't quite reach his sockets. “thanks, kid. just… see what you can dig up. i remember some things about gaster. fragments. stuff that doesn’t feel like it should belong to me.” He shakes his head. “but you—” he motions to Alphys, “—you’ve got the brain, and frisk’s got soul theory down to an art. if anyone can figure out what we’re up against, it’s you two.”

Alphys straightens a bit at that. It’s not praise—not really—but it’s a vote of confidence, and right now, she clutches it like a lifeline. Her mouth twitches into a shy, unsure smile, and she nods.

Frisk signs and speaks at the same time. “We’ll find out how to stop him.”

“good.” Sans rubs at the back of his neck, then exhales sharply through his teeth. His voice drops even lower, almost too soft to hear. “just—one thing.”

Both Alphys and Frisk look at him.

“if you find anything. anything at all about me. or papyrus. about… what he did to us—” He cuts himself off, jaw clenched. “don’t tell pap. don’t even hint.”

There’s silence.

Frisk nods slowly. Alphys frowns but doesn’t protest.

“i don’t know how much he remembers,” Sans continues, still quiet, almost ashamed, “but it ain’t all of it. and i know it’s selfish but… i want it to stay that way. i don’t want him carryin’ that weight. not again.”

There’s something broken around the edges of his smile now. Not the usual cracks. Not the usual exhaustion. It’s older. Deeper. Something that doesn’t heal all the way, no matter how much time passes.

Frisk steps forward and signs slowly: “He’s already carrying too much.”

Sans nods once. “yeah.”

They don’t say anything else. There’s nothing to say. Frisk squeezes his sleeve once before turning. Alphys gives Sans a look—uncertain, anxious, but determined—and the two of them move down the hallway toward the locked room. The one nobody wants to look at too closely. The one that hasn’t been touched since the collapse. The one that still hums with quiet power, like something waiting behind it is alive and listening.

Alphys has to hack the lock. It’s old tech—pre-Collapse—but still reinforced with layers of code she’s only half familiar with. Her fingers shake on the keyboard she’s rigged into the wall panel, sweat beginning to bead at her temples despite the coolness of the hallway air. Her glasses reflect the soft blue glow of the screen, the blinking cursor like a heartbeat, tapping time against her mounting anxiety. Every few seconds she glances to the side, half expecting the lights to flicker or some hidden alarm to trip.

Frisk stands beside her, close enough that she can feel the steady rhythm of their breathing. Their gaze never leaves the door. They’re watching, alert, shoulders set in quiet readiness. One hand is flexed at their side, the other hovers slightly, ready to sign, ready to speak. Their presence doesn’t chase away the knot in Alphys' stomach, but it helps. She’s not alone. Not like before.

The final layer of code decrypts with a soft, mechanical click. The lock disengages, and the door hisses open with the reluctant breath of something long buried.

Inside, it’s cold. Not the chill of AC, but the still, dead cold of air that hasn't moved in years. The darkness is thick, oppressive, like it’s soaked into the concrete and metal. The lights don’t come on. Alphys reaches into her pocket and pulls out a flashlight, flicking it on with a shaky thumb.

The beam cuts through the dark.

Stark metal walls, stained tiles. Dust swirls in the light. A table sits in the center of the room, bolted to the floor. The leather bindings—two on each side, one across the center—are frayed at the edges, ends stretched and warped as though something had pulled against them with relentless, inhuman force. The straps are stained in places, the metal buckles worn.

They stop in front of it.

Alphys stares at the table and sways slightly on her feet. Her voice is barely a whisper.

“I think I’m gonna be sick.”

Frisk doesn’t say anything. Their expression sharpens, lips pressed into a hard line. They step closer, letting their fingers skim along the edge of the table—just once—then move on. Determination replaces disgust in their eyes.

They make their way to the far side of the room where a long observation desk waits, dust-coated and buried in paper files, data chips, old monitors. Frisk starts pulling open drawers, flipping through their contents with efficient, practiced motion. Alphys joins them after a moment, eyes still darting back toward the table as though it might lurch or scream.

A minute passes. Then another.

The silence is broken by the soft, unmistakable echo of footsteps in the corridor. Alphys freezes, fingers tightening on a file she’s half-read. Frisk lifts their head.

The door creaks open. Undyne steps inside.

She’s quieter than usual, shoulders squared, magic flickering faintly behind her eye like a fuse straining against its limit. Her gaze falls immediately on the table. She stops in the doorway, and her jaw works visibly, teeth clenched tight.

“Shit,” she breathes, her voice rough. “He really used this, didn’t he?”

Neither Alphys nor Frisk answers. The room does not need it.

Undyne walks in slowly, steps heavy against the tiles. Her hand brushes the back of her neck, fingers flexing. There’s dust on her boots, a cut on her cheek. She looks tired.

Alphys clears her throat and glances up, voice low. “How’s Papyrus?”

Undyne’s eyes flick toward her. She sighs, dragging a hand down her face, then leans against the edge of the desk.

“Sans wanted to talk to him. Said I should come find you two.” Her voice softens just slightly as she adds, “Told me you’d be here.”

Frisk nods once. Their hands move, signing deliberately: We’re looking for anything on Gaster. His research. His magic. Weaknesses. Anything.

Undyne watches their hands, nods in understanding. “Right. Files on the bastard.” She exhales through her nose, short and sharp. “Great.”

Her hand runs over her face again, and she mutters, “He’s basically a walking void ball. How the hell do you even kill that?”

Frisk tilts their head, signing: We figure out what he made. Then we find out what he feared.

Undyne barks a laugh—short, bitter. “You think he feared anything?”

“Maybe not,” Alphys says quietly. She’s still flipping through files, eyes darting from line to line. “But he documented everything. It’s… it’s what he did. His need for control, for perfection. It’s in here. Somewhere.”

Undyne looks down at her, something fierce and protective flashing behind her eye. She opens her mouth, then stops. Instead, she walks over, rests a hand on Alphys' shoulder. “You good?”

Alphys nods without meeting her gaze. “Yeah.”

Undyne exhales slowly. “Then let’s get to work.”

She pulls up a second chair and begins rifling through the files beside Frisk. The three of them work in silence, the only sound the flutter of papers, the low hum of old machinery.

The files are dense. Most are written in Gaster’s jagged, impatient hand, full of symbols and references that only Alphys can decode. Frisk scans each page as they go, eyes sharp and unblinking. They pull one page out of a folder and tap it, holding it up to Alphys.

Alphys takes it and squints. “This is… a sequence. Genetic? No. Not quite. It’s… soul-bound parameters. He was trying to recreate a fusion event.”

Frisk signs, Fusion? Between souls?

Alphys nods. “I think so. It’s unstable. Extremely unstable. But he was trying to control it. Trying to force different soul types into alignment. See here—” She gestures to a line of hand-drawn charts. “This is Determination. And this one… that’s Fear. That’s not even supposed to be a standalone trait.”

“Fear?” Undyne’s voice cuts in sharply. “You can make a soul outta fear?”

“He could,” Alphys says grimly. “Or he tried.”

The room falls silent again. A cold draft snakes through the cracked tiles, stirring dust along the floor.

Undyne hisses through her teeth. “I swear to Asgore, when I get my hands on him…”

Her fists clench. Magic begins to crackle faintly from her fingertips.

Alphys places a gentle hand on her arm. “Undyne.”

The taller monster stiffens, then lets out a slow, shaky breath. Her muscles unwind, inch by inch. She nods once, jaw still tight.

“Right. Right. Focus.”

Frisk watches the two of them, then returns to the files. They pull out a binder—older than the rest—and open it. Inside are medical logs. Procedures. Pages of numbers. Scribbled corrections. One section is marked: S-1.

They stop.

Their hands hover for a second, then slowly begin to turn the pages.

Vitals. Neural scans. Restructuring of soul channels. Experimental nerve bypassing. Memory inhibitors.

Frisk’s brows knit. Their throat works, once.

They set the binder aside.

Alphys notices. “What is it?”

Frisk signs, slow. Stuff on Sans. I’m not—he said not to—

Undyne raises an eyebrow. “Said not to what?”

Frisk hesitates. Then shakes their head.

Alphys gently moves the binder away, setting it aside without opening it. “We’ll come back to it. If he wants us to.”

Frisk nods.

They continue working, deeper into the piles of forgotten data and cold, sterile pages. Somewhere, beneath all this, there’s truth waiting. The shape of Gaster’s madness. His power. His fear.

And maybe—if they’re lucky—a way to stop him.

Alphys holds a folder like it’s radioactive. Her fingers tremble around the edges, knuckles drained of colour. She doesn’t sit. Doesn’t speak right away. Just flips it open, eyes darting, scanning, processing.

“I think…” Her voice is small, tight. She swallows. “We should look at this.”

She lays the folder flat on the observation desk, the artificial lamplight catching on the yellowed plastic sleeve inside. Diagrams—drawn with disturbing precision—show a pair of hands rendered in stark anatomical detail. Instead of palms, each one features a circular hole, etched with surgical neatness. Notes litter the margins, cramped and aggressive. Calculations. Observations. Phrases like “extraction tolerance” and “channelled void density.”

Frisk leans in. Their brows pull together. They don’t say anything at first. Just… absorb. There’s something quietly electric in their stillness, like a wire humming under skin.

“They’re his,” Alphys says. “Gaster’s. His hands.”

Frisk looks at the diagrams again. A long breath leaves them, like they’ve just stepped off a cliff’s edge and are waiting to see if they’ll fall or fly. They tilt their head, eyes narrowing faintly. Their voice, when it comes, is low and steady.

“He carved them out himself.”

Alphys nods slowly, face pale as paper. “It looks like… yeah. He did. He removed parts of his own body—gradually, systematically—and reworked them. Turned them into conduits.”

Frisk’s hand hovers over the diagram. Their fingers sign slower now, more deliberate. He used those holes. To control the void. To... make it listen.

They pause. Swallow.

Sans and Papyrus… Their signing hesitates. Their voice barely follows. “They were… made from that, weren’t they.”

Alphys looks away. She nods. And then, shakily, she adds, “From his body. And his soul. And… and his magic.”

She looks like she’s going to be sick again.

“The incubation notes are detailed,” she says, flipping the page. “I think he wanted—no, needed—absolute control. He incubated Subject One for two years. Sans. Then removed him for field tests.”

Her hands flinch at her own words, like they burn her. “Papyrus… Subject Two… was left inside for another four. Four years. Gaster made adjustments after Sans. It says here—” she flips to a heavily redacted sheet, eyes skipping over the blacked-out blocks “—he… corrected the errors.”

“Errors,” Frisk echoes. The word sounds like it’s been poisoned.

Alphys is barely breathing. “He never called them by name. Not once. Just ‘Subject One.’ ‘Subject Two.’ No affection. No acknowledgement. Just… tools.”

There’s a silence that drapes over the room like lead. Undyne leans against the wall, arms crossed, head tilted back slightly. She hasn’t spoken in a while, but now her jaw shifts and she pushes off the wall, pacing slowly.

“Of course he didn’t write his own damn weaknesses down,” she mutters, voice thick with disgust. Her eye flicks toward the diagrams, then the restraints on the metal table, then the dim lights above.

Her steps are tight, deliberate. Measured only by frustration.

“Guy was smart enough to hide every skeleton in every closet, then incinerate the house.”

She stops. The fingers of one hand drift to her neck and rest there—just lightly, like she’s reminding herself to keep breathing.

Frisk watches her. Then signs slowly. You okay?

Undyne gives a short laugh, no real humour in it. “Am I okay? No. Not even close. But that’s not important.”

She runs a hand down her face, stops at her jaw, and sighs hard through her nose. “You said you were looking for stuff on Gaster himself. His magic. Weaknesses.”

Frisk nods.

“Well.” Undyne gives a sharp, sarcastic smile. “Good luck. The guy’s a walking void-ball. It’s like trying to find the weak spot on a black hole.”

Her voice drops, hardens. “But when I do, I’m going to tear him apart.”

Her fists tighten. For a moment, there’s magic buzzing off her skin, fizzing faintly into the air. Blue and violet crackles in the stale room lighting.

Alphys steps forward, quietly. She doesn’t speak. Just places a hand gently on Undyne’s arm. Her presence alone seems to quiet some of the storm.

Undyne breathes again. Shakily. Then nods.

“Okay,” she mutters. “Okay. Let’s just… keep looking.”

Together, they shift to the drawers, files, old logs. It’s methodical. Quiet. Frisk takes a box of documents to a different desk and sifts through it, flipping with care. They find photos—some blurred, some horribly clear. Bone samples. Blueprints of containment fields. A scrawled note that says, “Soul stress under compression leads to instability. Contain or cull.”

Frisk reads it three times. Then closes the folder.

They move back to the others, holding it out. “He experimented on souls.”

Alphys nods, her eyes still on a thick binder. “He was obsessed with them. With how they could be stretched, split, rewired. He believed every soul could be modified into a different function.”

Frisk doesn’t answer right away. Their fingers twitch. What function were Sans and Papyrus supposed to serve?

Alphys falters. “I… I don’t know. But I think it’s here. Somewhere.”

Undyne’s voice cuts in, sharp and low. “Weapons. That’s what he wanted. No one spends six years growing people in tanks unless they want to control what comes out.”

Frisk is quiet. Their expression is unreadable. Then, softly: “He failed.”

It’s not a boast. Not even a claim. Just a quiet truth.

“He made Sans and Papyrus,” Frisk says, signing between words. “But they’re not what he wanted. They’re more.”

Undyne gives a wry smile. “Damn right they are.”

They fall into silence again, flipping page after page, the clock ticking softly somewhere in the background. Each document adds a piece. A sliver of something awful. Autopsies on void-corrupted bodies. Charts showing soul degradation rates. Surveillance logs of Sans as a child—alone, wandering test chambers with glowing eyes. Papyrus in a stasis chamber, monitored for emotional variance.

Frisk feels bile rise in their throat. They push it down.

There’s a note tucked at the back of one folder. Scribbled, rushed. “Too much of me in them. Unpredictable.”

They read it aloud.

Undyne leans in. “Too much of him? What does that mean?”

Alphys frowns, flipping through pages. “Maybe… maybe he gave them more than just magic. If their souls are partially his, then there might be… echoes. Personality fragments. Things he didn’t account for.”

Frisk's hands are tense on the desk. They’re not him.

“No,” Alphys agrees, softly. “They’re not.”

Undyne grits her teeth. “Still. If he is part of them… what happens if he comes back?”

Frisk looks at her. “We stop him. No matter what.”

Undyne meets their eyes. Then nods.

“I’m with you.”

They return to the logs. The hours pass in silent flickers. Folders laid open, then closed. Data catalogued. Frisk never stops moving—never stops reading. Their determination is steel-forged. Undyne’s energy grows tighter the deeper they dig, her fury pressed down under a layer of focus. Alphys doesn’t speak much anymore. Her brain is elsewhere—calculating, decoding, stringing fragments of horror into some kind of map.

And at the centre of it all: Gaster. Not just a man. Not even a scientist. A force. A ghost woven through every page. Every experiment. Every pain-etched memory.

He’s not dead. Not yet.

Sans enters the room, his frame outlined by the doorway, stiff and shadowed. There's a subtle tension rippling through the air, thick enough to catch on the edges of breath. The overhead lights hum above them, dull and uneven. Papyrus follows a step behind, his hands clutched tightly together, fingers curling and uncurling with mechanical rhythm. His gaze is unfocused, bouncing from corner to corner, finally settling on the centre of the room with visible effort.

No one says a word at first. The silence is brittle.

Sans’ eyes — dimmed pinpricks of blue and white — hover too long on the table. On the folder. On the scattered diagrams and papers they all already know too much about. His expression doesn’t change, but something in the air contracts around him. Then, he blinks slowly, and his shoulders shift with a visible breath, the first movement he’s allowed himself.

“... i feel strong enough to get us outta here,” he says.

The others don’t respond right away. Alphys looks up, startled, uncertain whether she misheard him. Papyrus shifts beside his brother, like he might speak, but doesn't.

Undyne crosses her arms. Her brow furrows, jaw ticking. “I thought we were gonna take Gaster down.”

Sans’ stare doesn’t lift from the floor for a beat. When it does, his face looks worn. There’s a tension in the corner of his mouth that betrays the coolness of his tone.

“we can’t. not like this. we ain’t ready.”

His voice is quiet. It isn’t the mutter of someone dismissive, but the honest, lead-heavy conclusion of someone who’s seen the edges of something too large to name.

“We need to regroup,” he continues. “go back. look all this over. it’s not somethin’ we can wing.”

Frisk stands beside Alphys, watching the way Sans’ fingers tremble slightly as they curl at his sides. They glance at Undyne, whose hands have balled into fists. Her jaw clenches. She doesn’t say anything yet — not immediately.

Then, like a splinter snapping under pressure, the voice cuts through the room.

“You always were a coward, Subject One.”

The lights flicker.

Papyrus jerks a step back instinctively. Alphys freezes with a small, sharp gasp. Frisk’s eyes snap to the far end of the room, to a shape moving in the shadows like smoke under glass. Undyne’s head whips around, teeth bared.

The figure coalesces.

It’s Gaster.

But not the garbled mess from before — not a glitch in the air, not a smeared memory. His silhouette is sharper now. The angles of his body remain strange and disjointed, but they no longer fragment entirely. His face is visible — clearer, as though finally pulling itself into one timeline. The empty sockets are lit with something... cold. Calculating. Real.

His mouth moves, forming words before the sound even arrives.

Sans reacts instantly. He steps forward, putting himself directly in front of Papyrus, his stance defensive without needing to raise a hand. The tension pouring off him is a solid thing now, like gravity spiking.

Undyne summons her spear with a fluid flick of her wrist. The blue light hisses into life, her stance braced and ready.

Gaster’s gaze moves lazily toward her.

A sharp flick of his wrist — almost dismissive.

The spear rips from her hand and clatters across the floor, skidding against the wall. The impact rings.

Undyne flinches, swearing under her breath. She starts toward it, but Gaster tuts.

“Petulant,” he says, his voice rippling at the edges like the reverb of a poorly tuned instrument. “There’s no need for such theatrics. I haven’t come to harm you.”

Sans doesn’t move. His voice is low, flat.

“bit late for that, pal.”

Gaster’s smile twitches, a sliver of something dark.

“I only want the rest of my soul,” he says, tone casual — as though discussing a misplaced item. “That’s all I’ve ever wanted.”

The air drops a few degrees.

Frisk, standing just behind Alphys, feels something pull taut in their chest. Something about the words. The rest of his soul.

They look from Sans to Papyrus.

They understand.

It’s them. Sans and Papyrus. They’re the missing pieces.

Alphys says nothing, her lips pressed into a line too tight to speak through. She’s pale again. Paler than before, if possible.

Gaster turns his gaze toward Frisk, the smile he wears stretching — too wide, too long. It flickers, jumps, corrects itself. The glitch runs across his shoulders, like a static ripple in a television feed.

“You understand, don’t you?” he says, voice dipping into something smooth. “Intelligent little human. You’ve put it together. It’s all there in the documents. I was incomplete. Flawed. My soul, fractured. And I... refined the pieces.”

He lifts a long-fingered hand, the tips faintly pulsing with ghost-light.

“Subject One and Subject Two,” he says, like reciting from memory. “Reconstructed with care. Magic, body, soul — all shaped in the cradle of innovation. Years of work. And it worked, didn’t it?”

“they’re not yours,” Sans says, sharp. It’s the first edge he’s let into his voice.

Gaster’s gaze turns on him. Slowly.

“I made you,” he says, tone laced with a glimmer of genuine awe. “Both of you. My finest work. The culmination of every sacrifice I ever made. You don’t understand what that means. How can you, with so little of me left inside you?”

His face twists slightly. Not anger — not yet. But something is building beneath the surface. The lights flicker again.

“it means jack,” Sans replies, stiffly. “doesn’t matter what you say. doesn’t matter what you think. we ain’t yours. never were.”

Papyrus steps forward, still silent. His eyes are on Gaster, wide — but not with fear. There’s something colder there. Determination. Sadness. A recognition that claws somewhere deep.

Frisk shifts their hands and signs, their voice soft as they speak.

“He’s wrong. You’re not fragments. You’re whole.”

Papyrus glances at them, and nods once.

Gaster doesn’t seem fazed. He smiles — patient, indulgent.

“You think I’m here to fight?” he says, turning slightly, folding his hands as if in lecture. “No. No, I’ve tried that. I’ve learned. Conflict leads to nothing but instability. And I can’t afford to destabilize further. Not now.”

He flickers again — more visibly this time. Like a cut in a film reel.

“But I need what’s mine,” he continues, the warmth draining from his tone. “You’re not safe. Not like this. The energy inside you — fractured. It’s incomplete. Dangerous.”

His head jerks sharply — once, like a glitch skipping a frame.

“I can feel it. The longer you exist this way, the more entropy you generate. You think you’re stable. You’re not. You’re ticking bombs. Unknowing catalysts. This world, this plane — it’s warped around you already.”

The words fall like ice.

Undyne looks at Frisk, then at Sans.

Frisk narrows their eyes. Their fingers twitch, ready to sign again, but they speak instead — their voice steady:

“You’re lying.”

Gaster’s smile disappears.

Sans steps forward. Just a small step. But it’s loaded with weight.

“you want us scared. want us to doubt it. but you made one mistake, doc.”

Gaster’s head tilts.

Sans’ eyes gleam.

“you made me smart.”

There’s a breath of silence.

Then Gaster’s figure begins to tremble.

Not with rage — not at first. But the composure begins to crack.

“I made both of you,” he says, and the words come out wrong — layered, like overlapping tracks out of sync.

“You are mine.”

The air around him distorts. The edges of the room ripple slightly, warping like heat haze. The light above them buzzes, then sputters.

Alphys backs up a step. Undyne crouches slightly, reaching for her spear again, and Frisk moves to stand nearer to Papyrus.

But Sans — he doesn’t flinch.

“not anymore,” he says.

The glitch surges.

Gaster’s mouth opens — too wide — and the lights die with a sharp snap.

Darkness floods the room.

Only the sound of breathing remains — until the hum of something beyond sound begins to build, a keening, dissonant pitch that rattles behind their skulls.

Frisk grabs for Papyrus’ hand.

And the air, thick with pressure, begins to shatter.

Chapter Text

Frisk blinked.

The air shifted. Not with the sound of wind, or the flicker of any light—just a sudden and complete transition, as if the moment had been edited out of reality itself. The sensation of Gaster’s voice, of his looming presence, that sickening proximity of something not entirely real but unbearably present—it was gone.

And they were back.

The walls around them were familiar now: steel and white, the quiet hum of the room's systems steady and unbroken. The sterile chill of the Observation Room clung to their skin again, reality neatly reassembled around them as if it had never fractured.

For a second, Frisk didn’t breathe.

They stood stock still in the centre of the room, watching the others slowly come to terms with the shift. Alphys, closest to the wall panel, clutched her notes in shaking hands. Undyne was upright and tense, eyes darting across the corners like a soldier expecting the ghost to reappear.

And then their gaze found the brothers.

Sans had blinked too—slow and sharp. The furrow in his brow deepened with every second. His jaw was clenched tight. Frisk could see it in the line of his skull, how the tendons in his neck had drawn taut with unspent fury. Not the slouching, half-lidded calm he wore like armour. No, this was someone bracing for war.

Behind him, Papyrus hovered like a shadow unsure where to fall. His shoulders were pulled back, alert. Eyes bright with something that looked almost like belief. Hope. It was faint, but it was there, pushing past the tension in his spine. His gaze was trained on his brother, always on Sans—as if, in the crack of that second, he'd seen something awaken in him.

Frisk raised a brow.

Alphys met their eyes and gave the slightest nod. A quiet gesture of agreement—barely a motion. But it said enough. They weren’t ready. Not for what was down there. Not yet.

“If Sans is ready…” Alphys’ voice was thin, careful. “We should… we should head back. We can’t do anything like this. Not in our condition. And he won’t leave the Core area, not now. We can regroup—”

“that never stopped him before,” Sans muttered.

The way he said it—it wasn’t bitter. It wasn’t even sharp. It was tired. Old.

As though he'd said it before.

He took one long look around the room. Not at the walls or the blinking lights or the consoles still faintly flickering, but at them—his team, such as it was. Alphys, uncertain and trying. Undyne, ready to fight even if she couldn’t win. Papyrus, somewhere between a question and an answer. And Frisk, watching, always watching.

“I’ve got an idea,” he said.

And he turned.

No grand declaration. No dramatic call to arms. Just the solid weight of decision behind each step as he left the room, the soft echo of his bones tapping against the floor.

Papyrus moved almost instantly after him, like he couldn’t stand to let the distance grow.

Frisk caught the way his expression shifted. Papyrus didn’t look at anyone else—just Sans. He followed him as if his brother’s presence alone kept him upright, as if walking beside him now made something that had been broken feel whole again.

Maybe it was memory. Maybe it was something deeper, some invisible thread from when they were just two kids in a world that didn’t see them.

The rest of them exchanged glances—Undyne with a twitch of her brow, Alphys with a worried crease between her eyes—but they followed.

They wound through halls the colour of bleach and static, the buzz of old overhead lights brushing against their ears. No one spoke. Sans moved with something close to purpose, something heavier than his usual limp drag of movement. And when he reached the door—one marked not with numbers but with faded ink and a long-forgotten plaque—he didn’t hesitate.

Gaster’s office.

It was locked, of course.

But a faint blue glow pulsed at Sans’ fingers as he flicked them toward the mechanism. A click. A hum. The door hissed open.

The room was dark.

Not dark like shadowed corners, but dim in the way of a space long disused—screens blank, monitors powered down, paper scattered and yellowed at the edges. There was dust on the floor in the shape of something that had once stood there. Blueprints half-crushed beneath the heel of time.

Sans stepped inside and immediately made for the desk. He didn’t hesitate—opened drawers with a flick of telekinetic force, skimmed fingers over control panels until they sparked and whirred to life. One by one, old data screens booted up, blinking with fragmented schematics, corrupted logs, old files named in hexadecimal and half-familiar strings.

Papyrus lingered just behind, cautious.

“I didn’t know you were ever allowed in here,” he said softly, voice a little smaller than usual.

Sans snorted, but there was no real humour in it.

“wasn’t,” he replied, fingers still moving.

He didn’t look at Papyrus.

“used to sneak in, though. when the doc was… busy.”

He trailed off.

The glow from one monitor pulsed faintly against his skull, shadows deepening in the hollows of his eye sockets. He turned slightly—just enough to glance back at his brother.

The grin he wore then was thin, almost fragile.

“i’d mess up his notes. reroute the wires. swap labels, reverse schematics. took ‘im weeks to figure it out. drove him nuts.”

A beat.

“meant he was too busy tryin’ to fix junk to mess with us.”

Frisk, just a few paces behind them, felt their stomach tighten.

Alphys looked sharply at Sans then, her mouth open like she might say something, but she didn’t. Her eyes dropped to the floor instead.

Papyrus said nothing.

He just watched Sans.

And Sans… kept working.

He pulled up logs, internal schematics, partial blueprints of the Core’s deepest levels. He skimmed through diagrams half-corrupted by time, found references to energy states, void anomalies, fractal soul matrices—notes that rambled in Gaster’s distinct shorthand, impossible for most to read. But Sans could.

“he’s not stable,” Sans muttered. “he’s more complete than he used to be, but not stable. not tethered.”

Undyne leaned against the wall, arms crossed.

“Great. So he’s a ghost with a body. What’s the plan, Sans?”

He didn’t look at her.

“we need to find the part of him that’s still missing. it’s probably the only reason he hasn’t gone full meltdown yet.”

“And what’s that?”

Sans didn’t answer.

Instead, he stared at the screen, hand curling slightly.

Frisk moved closer. They could see the image on the monitor now. It was a soul chart. Fragmented, glitching—an image of Gaster’s essence. It wasn’t whole.

There were two voids. Two pieces missing. And their shapes…

Frisk swallowed.

They turned to Papyrus. Then to Sans.

The realization landed like a quiet thud behind their ribs.

Gaster had said it himself.

“I only want the rest of my soul back.”

Frisk signed slowly, fingers slightly shaky. It’s you. Both of you.

Sans glanced over, and for a second, the edges of his grin cracked.

“yeah.”

Papyrus took a step back.

“Wait—what? What do you mean, US?”

Frisk hesitated, then gave a tiny shrug. It wasn’t exactly a full explanation. But it didn’t need to be. Not yet.

Sans’ eye flickered with the familiar glow of blue.

“we’re pieces he ripped off. fragments. he built us from what was left of him.”

Papyrus staggered back another step.

“NO,” he said, louder now. “That’s—That’s NOT RIGHT. I’m not… I’m not him. I’m ME.”

“yeah, you are,” Sans said quietly. “we both are. but we came from him. that’s the piece he’s missing.”

Undyne’s voice cut through the tension.

“And if he gets that back—?”

Sans didn’t answer.

But he didn’t need to.

The silence hung for a moment. Then Sans turned back to the screens.

“i’m gonna find where he’s weakest. the spot in the core where he’s anchoring himself.”

Frisk signs as they speak, hands moving in tandem with their voice. “You mean we. We are gonna find where he’s weakest.”

Sans glances over at them. For a moment, something in his expression falters—just a hairline crack in that usual deadpan mask. But his eyes shift to Papyrus, who meets his gaze with quiet resolve. A slow nod passes between them like a silent vow, old and deep. Sans turns back to Frisk and gives a half-hearted shrug, a silent concession. They’re in this together. Whether he wants it or not, he’s not alone anymore.

He steps forward and taps at the monitor. A stream of corrupted data scrolls across the screen, flickering occasionally with stabilised segments—names, files, strings of code half-lost in distortion. He types something quickly, fingers working from muscle memory, not needing to check what he's doing.

Then, a window opens.

An audio log. Sans doesn’t say much, just clicks on it. The title is obscured—only “Audio Log XXXX” remains legible. Everything else glitches out, corrupted or overwritten. Alphys frowns at the distortion, her gaze scanning the mess of characters like she might will it into clarity. But Sans leans in, steady hand moving the cursor to the play button.

“This one’s from one of our... chats,” he mutters. “Right after a test. He used to call it the recovery phase.”

He presses play.

The speakers crackle, feedback whining faintly before settling into the sound of static and breathing.

“Audio Log XXXX,” Gaster’s voice declares, clinical, distant. The way he says it makes Frisk’s skin crawl. There’s something dispassionate about it, something that lacks even the cold professionalism of a scientist. It's mechanical, recited. Detached.

“Time of recording: unknown. Date: corrupted. Experiment series 347. Soul resonance test, post-intervention. Initiating recovery phase. Subject One—state your condition.”

There’s a pause. Three seconds. Five.

“HP 1, DEF 1,” a younger voice answers, dry and irritated. “C’mon, Doc. It’s the same. It’s always the same.”

The voice is unmistakable. Tired. Worn thin. Sans, years younger. Bitter around the edges.

Alphys leans forward. Her voice is soft, barely audible. “That was you...”

Sans doesn’t respond. His expression doesn’t change. He just keeps listening, jaw clenched, eyes fixed on the screen like he could burn through it.

“Subject One is stable, but depleted,” Gaster continues. “Magical signature consistent with pre-experiment thresholds. Notable deviation in soul fracture pattern—progressively worsening.”

There’s a soft scoff from the recording. “Didn’t think you had one,” Sans says, and it’s impossible to tell if the snark was meant to protect himself or provoke Gaster.

Gaster, however, only sighs. “As Subject One is an extension of my soul, its degradation reflects the instability of my own magic. I postulate that the continued splitting of soul matter during experimental phases has resulted in a loss of cohesion—one that may be irreversible without full retrieval.”

Frisk’s brow furrows. They glance at Papyrus, who looks stricken, like something fragile in him is fraying.

Gaster's voice drones on. “Subject One’s resonance pattern has absorbed the overflow of magical deterioration. As such, his manifestation of inherited magic grows erratic. Unpredictable.”

Sans pauses the audio.

He doesn’t speak for a moment. The weight of what they’ve just heard settles differently than before—sharper, edged like glass underfoot.

Then he exhales, voice low. “Without gettin’ his soul back... the pieces he’s missin’ from me and Papyrus... he’s gonna dust. Eventually. Just a matter of time.”

Papyrus steps forward slowly, posture tense. “You said he—he anchored himself in the Core. But if he’s still incomplete, if his soul’s unstable... then maybe he can’t anchor anything. Not for long.”

“He’s desperate,” Alphys murmurs. “That’s what this is. He’s spiraling. The timelines, the loops, the experiments—he’s trying to fix something he broke a long time ago. Trying to put himself back together.”

Frisk signs quickly: We need to find the place where he’s most unstable. If we can break that anchor, maybe we can force him to stop.

Sans nods faintly. “Yeah. That’s the plan.”

He turns back to the console and begins pulling up Core schematics. It's slow work. The files are fragmented, corrupted just like the rest of the logs, but there's enough to work with. With every line of code he patches together, a piece of the Core’s structure unfolds—maps, surveillance grids, power circulation patterns.

Frisk watches Sans work with a kind of quiet awe. It’s easy to forget, sometimes, how deeply he understands this place. How much of it he must have memorised. He moves like someone navigating a house he grew up in, even if half the doors are missing now and the lights keep flickering.

“this is it,” Sans mutters, pointing to a pulsating red cluster of pixels at the base of a power conduit junction. “it’s not the centre, but... it’s close to where the Core fractures out. like a nerve ending. if he’s hiding anywhere, it’s gonna be here.”

Alphys leans in. “That section was sealed years ago. After the—after the first melt. But if he’s drawing power from the original lattice, he could be using the residuals. There’s no surveillance down there anymore.”

Papyrus inhales sharply. “Then... we go.”

Sans nods, though he doesn’t look thrilled about it. “yeah. we go.”

They gather what they need—Alphys quickly assembling a scanner calibrated to detect soul resonance fluctuations, something barely held together with soldered wires and stripped copper. Frisk checks their bag, making sure their notebook and small set of healing items are intact. The bandages are a bit crumpled, but they’ll do. Papyrus doesn’t carry anything; he simply squares his shoulders, spine straight, hands flexing at his sides like he’s preparing for battle.

The corridor to the lower lattice is barely lit, the walls pulsing faintly with residual magic. It smells like burnt ozone and dust. The floor trembles underfoot with every cycle of the Core’s internal pulse.

They walk in silence, this time not oppressive or heavy—just tense. Alive. The air is electric with expectation.

Frisk walks beside Sans, who hasn’t spoken in minutes. Every so often, they catch him glancing at the scanner in Alphys’s hands. The further they descend, the more erratic the readings become.

It’s working.

They’re getting close.

Papyrus stops suddenly.

“There,” he says, voice tight. “That door. I remember it.”

The door is partially open, its hinges twisted, like it had been torn open rather than unlocked. Beyond it is darkness. Not just unlit—something about the void feels wrong, like it resists the idea of being seen.

Sans steps forward. “this is it.”

He raises a hand, summoning a small flicker of blue light—just enough to cast long shadows against the corridor walls. Frisk steps beside him, heart beating fast.

They move into the chamber.

And then everything changes.

Undyne slows her stride, eye catching on something out of place. Not just rubble or strange machinery or the Core's signature burn of amber light. No. A walkway. Thin and precarious, suspended above the Core’s open reactor, a jagged platform of metal and tempered glass cutting a path into the very heart of the facility. The air hums hotter here. Everything vibrates at a low frequency that crawls up her bones.

She reaches a hand out and stops Sans. “That wasn’t there before.”

“No,” he agrees, voice tight. “It wouldn’t’ve been.”

Alphys steps up behind them, mouth slightly open, brow furrowed in disbelief. “That leads… right above the main power chamber. That’s where the control interfaces are… or were. But no one’s maintained this in—”

“this is where gaster died,” Sans says, and it’s so calm that the words come out almost like an offhand comment. He doesn’t look back at them. Just stares at the walkway like it’s a long-forgotten grave.

Undyne’s eyes snap to him. “What do you mean ‘died’?”

Papyrus stiffens at her side. “I—I didn’t know that’s how he—how it happened. One moment he was in our room, and then…” His voice drops. “And then Sans was at the door. He dragged me out of the lab. Wouldn’t say a word. The next thing I remember, we were in Waterfall. And then we were found by the King himself.”

Frisk watches them all from just behind Alphys. They’re quiet, one hand held loosely against their chest, fingers twitching. Their gaze tracks the walkway but darts often to Sans, who hasn’t moved.

Sans takes a slow step forward, tapping the metal underfoot with one foot like he’s testing for ghosts. “down there,” he says, motioning with a flick of his hand toward the far end of the walkway. There, at the metal’s edge, is a long, ugly scorch mark. It eats into the steel, edges jagged, as though something had detonated just above it.

“that’s where it happened. he dragged me down here during our last ‘test’. he was rambling, saying it was all a mistake. that he could fix it. would fix it.”

Undyne bristles. “Fix what?”

Sans doesn’t answer her directly. Instead, he keeps walking until he’s halfway across the platform. The Core pulses beneath them, lighting his face from below with gold and crimson like a stage light in a theatre he never asked to be cast in.

“he said he was gonna grind me and paps to dust,” he says, eyes still locked forward, tone flat. “build us again and again till we were perfect. the weapons he needed. said it was all for the future. the war. survival. said he’d sacrificed part of himself to make us.”

Alphys gasps sharply, her hand flying to her mouth. “That’s—what he meant in the logs, about fragmenting his soul…”

“he was erratic.” Sans shrugs, but it’s brittle. “hadn’t slept. hadn’t eaten. eyes bloodshot. one of them was already… wrong. flickering like a static feed. he dragged me all the way down here and just kept talking, to himself more than to me. said i’d failed him. that paps had. that he regretted making us, not ‘cause it was wrong, but ‘cause we weren’t what he wanted. what he needed.”

The floor beneath them buzzes faintly. No one speaks. Even the distant sounds of the Core’s hum seem to withdraw.

Papyrus is shaking slightly. “Brother… what happened next?”

Sans finally looks at him. Not over his shoulder, but fully turns, shoulders hunched, eyes shadowed beneath his brow.

“he threatened you.”

Papyrus swallows hard.

“said he was gonna dust us both. for parts, probably. or just… get rid of the evidence. clean the slate.”

Frisk steps forward then, lips pressed together, eyes sharp.

Undyne’s voice cuts the stillness. “So you killed him.”

Silence again. This time not out of awe or grief or fear—but understanding.

Sans looks down at the scorched metal, then nudges it with his foot. “i didn’t mean to.”

He says it so simply.

“but i knew he was dangerous. and i was scared. not just for me, but… for paps. for everyone. guy was falling apart. his magic was going haywire. he wasn’t even blinking right anymore.”

His gaze lifts slowly to the far wall. There, barely visible in the dim lighting, are more scorch marks—faint, scattered along the walls in patterns like spirals, sharp-edged and burned deep. They crawl up the metal supports and arc across console panels.

“why do you think i called them gaster blasters?” he asks, and his mouth twitches like he might be about to smile, but it never reaches his eyes.

Undyne lets out a sharp breath—half laugh, half exhale. “You’re kidding.”

“nope,” Sans says. “first time i summoned one, it was during that fight. copied the design from one of his constructs. they looked different back then. spikier. didn’t even work right most of the time. unstable.”

He closes his eyes for a moment. A pulse of Core energy flickers through the chamber. When he opens them again, the look is heavier—less guarded.

“it was a long fight. i tried to talk him down. tried to run. but he was determined.”

His eyes flick briefly to Frisk, then away.

“used that against him. got him talking. made him second-guess. cornered him here, right at the edge. he was standing where that scorch mark is. hands clinging to the railing.”

Papyrus takes a half step forward, staring at the mark.

“we looked at each other,” Sans murmurs. “i still remember his face. the way his mouth moved but no sound came out. like even then, he couldn’t say it.”

He doesn't finish the thought.

The silence this time is quieter. Not oppressive—just patient.

Frisk approaches him slowly, lifting their hands. You don’t have to keep it all in, they sign. You’re allowed to feel bad. Even if it saved you. Even if it was right.

Sans breathes in. Out.

“doesn’t change what happened.”

No. But maybe it changes what comes next, Frisk replies aloud, soft. Their voice is steadier than it has any right to be.

He doesn’t say anything.

Alphys clears her throat gently. “That level of soul fragmentation… it must’ve destabilised the entire lab. That might be why so many of the timelines started—merging. It might be why you—why he—was able to access the Void in the first place.”

Sans gives her a sharp look. “you saying it was my fault?”

“No! I mean—maybe not just you,” she says quickly. “I’m saying it wasn’t just a one-way door. If he really fell in here, and his magic was that unstable, and he was that close to you and Papyrus…”

“a piece might’ve stuck to us,” Sans finishes.

Alphys nods. “Or a lot more than a piece.”

Frisk nods slowly. “Then we can use that.”

Sans stares at them. “use what?”

They hold up their hands again, fingers slow, deliberate. You have a tether. You’re a tether. If we want to reach him—if we want to end this—we follow it back. Find what’s anchoring him. Break it.

Sans huffs out a breath. “and if it pulls us in instead?”

Frisk shrugs. “Then we go in together.”

Undyne’s fist clenches. “Then we pull him out.”

The echo of her voice fades quickly into the low hum of the CORE around them, the distant thrum of electricity and burning magic pulsing beneath the grates. The air is warmer here, charged, as though every molecule of it remembers who built this place and what he left behind in its circuitry.

Papyrus steps forward, his bones squaring as he rises to his full height, posture suddenly steadier than it's been in days.

"I remember," he says, and there’s something firmer in his tone—something rooted. “I remember him talking about the CORE like it was his greatest invention. He used to go on and on about it. Not just how it worked, but what it meant. The convergence point of space and power, where the fabric of the Underground was thinnest. He said it connected everything.”

He gestures around them, fingers sweeping across the walkways and machinery. “The whole Underground... all of it... he tied it together with this.”

Frisk glances from Papyrus to the exposed consoles, their brows furrowing. Their hands lift instinctively, moving slow, deliberate signs.

Like he anchored himself?

Papyrus nods, tapping his skull. “Exactly! I think he may be tethered to the Underground itself. That’s why—why the CORE still feels like it’s breathing. Why the tremors are getting worse. He's not just trapped. He’s part of it now.”

Alphys, who has been mostly quiet since they arrived, finally speaks up. “That... actually makes sense.” She pushes her glasses up her snout with shaking fingers, then opens a monitor on the nearest terminal. The flickering screen shows code that flickers and jitters every few seconds, like something half-glitched, half-alive. “I’ve seen these patterns before. I thought it was just CORE instability—ambient anomalies. But if he’s tethered, if his essence got pulled into the system…”

She trails off, eyes wide, mouth slightly open. “That explains the tremors. And the inconsistent readings. The signals I couldn’t trace. They weren’t static. They were him.”

Undyne swears under her breath. “So what, we unplug him? Just hit the off switch?”

“No,” Sans says, voice low, even. He hasn’t moved since his confession, but now he steps forward, eyes half-lidded. “we lure him out.”

Undyne whips her head around to glare at him. “Absolutely not. No one’s being used as bait. I’m not letting anyone stand in front of that freak just to get his attention.”

“it’s not about letting,” Sans replies, still calm, but there’s a sharper edge behind his words now. “it’s about what works. we can’t pull him out by force. he’s buried too deep. but if we give him something he wants, something he recognizes... maybe we can get him to show his face.”

Frisk signs sharply, not even bothering to speak.

What would he even respond to?

Sans looks at them. There’s a beat of quiet, and when he finally answers, it’s not with a joke or a smirk, but with something grim.

“me.”

Papyrus flinches, but doesn’t interrupt. Undyne just stares.

Sans looks over his shoulder toward the deeper part of the chamber. The faint lines of scorched stone still mar the far wall where magic had once lashed out uncontrollably. “he made me. built me from code and dust and hope and madness. if there’s anything left of him down there... he’ll come for me. i’m the unfinished work.”

“Then he’s gonna try and finish you,” Undyne says, the words hard, flat.

“maybe,” Sans agrees. “but we won’t let him.”

Alphys folds her arms tightly, eyes darting between everyone. “Okay, assuming we could even get his attention like that, how are we supposed to interact with him? He’s not fully material. We don’t even know what we’re dealing with. A projection? A ghost? A sentient glitch?”

“Don’t care what he is,” Undyne snaps. “If he comes through, I’ll make sure he stays through. Permanently.”

Frisk's expression twists, and they finally speak. Their voice is soft but clear.

“He’s not going to stop just because we’re ready to fight.”

They pause. Their hands rise again.

He thinks he still has control. If we challenge that—he’ll lash out. He’ll do something reckless.

Sans nods slowly. “exactly. and we use that. push him outta hiding.”

Papyrus hesitates. “But what if he—what if he doesn’t stop? What if he drags you down with him again?”

Sans doesn’t answer right away. His gaze falls to the metal beneath their feet, then to the blackened edge where the railing gives way to open air and pulsing light. The spot where, years ago, he watched the man who built him fall into the very system that had consumed his mind.

“then we finish what we started,” he says.

Alphys sets up a crude rig near one of the control panels. Wires and cracked screens blink to life, drawing energy from the flickering heart of the CORE. A few of the panels are unstable, sparking intermittently, but she works quickly, typing commands with feverish precision. Her mouth twitches with every burst of static.

“This isn’t a proper conduit,” she warns. “It’s barely even safe. But if I can spike the signal... we might be able to catch his attention. If he’s still thinking in terms of systems and code, then he’ll see the breach as an opportunity.”

“or a threat,” Sans mutters.

“Either way,” Alphys says, not looking up, “he’ll notice it.”

Undyne paces behind them like a coiled spring, arms crossed tightly across her chest. “And once he does?”

“We talk,” Frisk says, stepping forward. “We tell him we’re not scared.”

Their voice trembles just slightly.

Sans gives them a half-smile. “he won’t believe it.”

“I don’t care,” Frisk replies.

Alphys flips a switch, and a shrill buzz echoes from the rig. Lights around the walkway dim, then pulse once, twice, before surging back on brighter than before. The hum of the CORE rises an octave.

“Okay,” she whispers. “It’s started.”

A gust of warm wind blows across the platform. It shouldn’t exist—there’s no airflow here. But still it comes, brushing against them with the feel of something alive, aware.

Frisk turns their face toward the wind. Their hands twitch at their sides.

Undyne doesn’t wait. She draws her spear from the magic at her fingertips and slams its butt into the floor. “If he’s listening,” she growls, “then he can hear me loud and clear: you hurt anyone, and I will take you apart atom by atom.”

“he’ll like that,” Sans mutters. “he loves a good threat.”

From the shadows of the chamber, something shifts.