Chapter Text
The skeleton's eyes are on Alphys' claws while she assembles the Sapphire Enhancer around his hand, his forearm, his exposed ribs; he's bare from the waist up. There's shortcut open to the Void nearby, to let Gaster help her through sign language. She's talking, but he's not listening.
Sans' sockets are on the present, but his mind is anywhere but.
It was quite a few months ago that he woke up like he'd been electrified, with other months' worth of memories suddenly clogging his already overfilled skull from his other self, the one that went through the Reset with Frisk. Months of wandering a dust-filled Underground, of monsters mourning relatives, of research into the kid's soul and the Void Extract taken from it, of its effects, of talking to the old forgotten Doctor Gaster through an Echo Flower tainted with the stuff. He remembers splitting the souls apart with the Extractor, Frisk's and what little was left of Chara's, and seeing Flowey, a warped puppet to Chara's will, tear across the entire Underground, trying to complete the job Chara began before he killed them in the Golden Hall.
Sans remembers going to the basement of Asgore's castle, to the Stasis Generator and the seven souls, and freeing them, and taking Frisk's. He remembers the pain of it, of his limbs splitting apart, of flesh forming underneath the bone-turned-carapace, and that heat, the vague not-warmth he'd always feel, the tug on his soul that told him when Frisk was in the Underground, come to a head as a scorching, blazing fire in his very core as their souls became one and the same. He remembers the kid's voice in his skull, and how he suddenly felt too big for his body, despite the bony fleshless wings and the hot flesh and blood filling his bones, bloating them like balloons, and the sheer power when he brought out his original Blaster and the thing was just as warped as him, bigger, sharper, covered in spikes and horns and flesh inside the expanded white shell.
Sans remembers passing through the faint, not-really-there chill of the Barrier with the other souls, and leaving them there for the abomination that Flowey and Chara had become to see, forever out of reach, as he himself just left them to their prison, powerless inside their little bubble of dust and rubble. He remembers walking outside under the dying sunset, remembers feeling the bite of the snowy cold on his bone-carapace, on the slivers of flesh and skin peeking through the joints. He remembers talking to Frisk, and the heat of Determination roaring through his new veins like wildfire, giving him a confidence he'd lost a long time ago. He remembers agreeing to the Reset, and his skull hitting the forest floor before his headless body did, and reality coming undone like when you take a thread and pull and unravel the whole fabric above it.
Sans remembers the Void. Unending black, thick as molasses and yet emptier than space itself, because at least space gives you something to look at, and cold by the sheer absence of temperature as a concept, along with time and space and anything that makes reality real and the Void its opposite; the antimatter to Reality's matter. He remembers talking to Gaster, or what little was left of the old skeleton, with his warped skull and drooping socket and hands melded together around nails that weren't there, holes on his palms that he used to show them, both Sans and Frisk, all the golden sparks, the Save Points, hanging in the not-air all around them, fake stars for a fake vacuum, because how can there be vacuum when matter itself doesn't exist?
And, finally, Sans remembers his promises to save both Frisk and Gaster. Or rather, the promises of his other, DT-fuelled self, that were foisted upon him when all these memories rushed into his skull at once and gave him a head-splitting migraine and jolted him awake all those months ago.
That very same morning Sans had jumped out of bed and through a shortcut, and found his way into the Ruins, and, yes, he's not afraid to admit it, kidnapped the human from right under Toriel's nose, almost literally. He hadn't been quick enough, they'd already managed to get dust on their clothes, but there was nothing he could do about that. Their LOVE wasn't high at least, that tug on his soul had only pulled him against a single nail instead of a whole bed of them. Like making a bed of pencil butts, those with the little eraser on the other end, but then putting one of them with the writing end pointing up and sharpened.
Since then, the human's been kept in this sort of cave Sans found high above the Underground, carved up into the ceiling of the titanic space monsterkind calls home by erosion or water or whatever. He'd found it, and tied the kid to some stalagmites, tied them so tightly they could barely even move their fingers and jaw. He hadn't, at first, but Chara kept finding new ways to hurt Frisk's body to try to kill them and trigger a Reset, and Sans had been forced to restrain them down to their teeth so they wouldn't bite their tongue off and drown in their own blood.
With the human safe and sound and, most importantly, away from Flowey's network of eavesdropping vines, Sans had turned to the matter of how to split Frisk and Chara again. He needed their soul for that, but he couldn't exactly kill them for it like last time, and his blue magic is nowhere near strong enough to let him tear it out of their body like the doc used to do with his subjects. But , Gaster had come up with a possible workaround back in the day. All Sans had to do was figure out how to build the damn thing without drawing Flowey's attention.
The skeleton's smile widens while Alphys works.
Heh, when he opened that first shortcut to the Void, the old doc had freaked out so much. It was a shot in the dark, quite literally. Sans could only open shortcuts to places he personally had been, and he hadn't really been in the Void, his other self had. But, as it turned out, the air split apart into the absolute black after only some slight resistance. He'd found a loophole. Gaster had fretted and worried and absolutely refused to let Sans put even the tiniest bit of bone over the threshold of the crack, and since nothing that wasn't him could get through the skeleton's shortcuts without touching him, Gaster was trapped on the other side of the invisible wall. But they could talk at least. Or rather, Sans could talk. Gaster had to use sign language to respond. There's nothing in the Void to carry sound, regardless of how capable of speech the warped skeleton may or may not be.
Even disregarding the fact that the blueprints were unfinished, Gaster had become a vital part of the little conspiracy that had formed between him, Sans and Alphys. He could keep an eye on Flowey from the Void, to make sure the flower didn't catch on to what was going on. He ensured the secrecy of their work, and without his help, the completion of the Sapphire Enhancer would've taken infinitely longer.
The Enhancer project had never left the drawing board, back when the Doctor was still... well, not alive so much as a part of reality. His status as a Boss Monster made his blue magic so powerful he could easily tear the soul out of his target's body, but in the offchance that the ability might be needed by a monster of less power, he'd come up with the concept of the Magic Enhancers: devices meant to tap into the energy of the wearer's soul and multiply it tenfold. Gemstones were to be inlaid into the structure, with the colors corresponding to the Soul Trait to be enhanced. Ruby for Determination, Amber for Bravery, Citrine for Justice, Peridot for Kindness (emeralds were too dark), Turquoise for Patience, Sapphire for Integrity, Amethyst for Integrity. A Diamond Enhancer had been intended as a non-specific alternative meant to heighten all of a monster's abilities at once, and with the discovery of the Void Trait by Sans, the Onyx Enhancer was also added to the project.
But they only need the Sapphire one, and Gaster was adamant about it being destroyed once it has fulfilled its purpose. They haven't even bothered making it look nice. The thing Alphys is putting together around Sans' arm and chest is nothing but thin, metal scaffoldings molded to the bone, supporting a mess of wires and tubes and little dark blue gemstones at carefully-calculated positions along his limb and across his ribs. The chest part was done first, and she's just finishing with the bits around the fingerbones when the skeleton's thoughts wander back to the present.
His gaze glides past Alphys' claws and goes to the shortcut he's been keeping open, but Gaster doesn't notice. He's looking at the lizard's work, meeting her periodic glances with nods and encouraging smiles to reassure her that yes, she's doing fine, everything looks correct, keep going.
Eventually, Alphys breathes a sigh of relief and sets down her tools. "A-all done," she says, running a hand over her brow to wipe (uselessly) at the sweat beading from under her scales.
Sans sits up straight and moves his arm, twisting it this way and that, bending the wrist, the fingers, making sure his movement isn't restricted. Once he's satisfied, he gets to his feet and splays out his hand toward Alphys. Her chest lights up with blue, as expected, but the Enhancer comes to life as well, thankfully. Sans can feel a sort of... like a grip in his soul, a cold iron hand that wraps around the bright white heart with the black spot that forms, all on its own, inside his ribcage. The little sapphires all shine like Christmas lights wrapped around his arm, and the tubes running from his ribs, up over his shoulder, past the elbow and all the way to his palm, fill with light as well, a smoky, hazy, shifting blue radiance like a neon sign that's at the end of its life.
His hand drops, and the light fades. Alphys lets out a breath she was apparently holding. "feel any different"? Sans asks.
"Um... m-maybe? I think the hold might b-be stronger."
Sans just hums.
He's looking at the mess of metal strapped to his arm. Then his gaze goes to the shortcut, and the warped skeleton beyond it, but Gaster shakes his head and smiles before Sans can do anything. NO POINT, he signs.
The skeleton just shrugs and looks at his hand again, then lets his arm drop. "guess now we just need to test it."
The looks he gets aren't any different from what he expected. Worry, and reluctance, in the glance Alphys and Gaster share. "we need to make sure this thing's working properly, don't we?" he goes on. "we only got one chance with this."
Alphys is fidgeting with her buttons. She stutters and mumbles something out, but it never forms into words. Gaster is wringing his hands, blending the half-molten bone together. Neither of them are looking at Sans.
The skeleton rolls his eyes. With a wave if his hand, the shortcut closes, but just before it does he can just barely catch a glimpse of the doc's worried, almost pleading look. Alphys looks alarmed as well, and when he turns around and another crack begins to split the air, she realizes what he's going to do one moment too late. "Sans, don't-!"
She's cut off by the shortcut closing behind him.
He's in Waterfall now, up on one of the secluded spaces that're out of reach from most easy footpaths, surrounded by rock like crooked fangs on the mouth of a great beast, the ceiling hanging low over him, dripping cold water onto his skull. He sighs and wipes at his head by reflex. "i know you've turned a new leaf and all, but it's necessary," he says to the velvety darkness around him; Gaster's watching, he'll get the message. With one last roll of his wrist to try and get the wires to behave, Sans sets off to find a test subject.
Even in the darkest, most remote corners of the Underground, even in places that not a single monster has ever set foot in, there's always this subtle, underlying glow, a faint light coming from nowhere and everywhere at once, leaving little to no shadows upon the most uneven surface. It's this ethereal glow that guides Sans around the blunt ends of stalagmites and stalactites, until he reaches the edge of the spiny plateau he's on and looks out over the glowing marsh below. He gets down on one knee and scans the bridges of land and wood crisscrossing over the shimmering water, marking each monster he sees in a mental map, looking for an isolated area, a lone wanderer, anything like that. After a minute or so, he finds it: a single moldsmal, quivering at its own faint reflection at the water's edge, on a little finger of land apart from the rest.
The skeleton's hand lifts. The gems light across his ribs, down his arm, one by one, cobalt smoke filling the tubes and entwining with his fingerbones. His eye flashes, cyan and yellow. The distance makes it harder, Sans has to aim carefully, he even puts the distant moldsmal between his middle and ring finger in his sight. But then he feels it, like an invisible tendril shooting ahead, reaching for his target. Blue springs up around the gelatinous monster, and before the thing can react Sans clenches his fist and jerks it back.
A tiny white blur is the only sign it worked, until the little soul stops dead mere inches from his knuckles, but he barely has the time to look at it before it dissolves into nothing. And where the moldsmal was now stands a little pile of dust that is easily scattered into the water by a passing wind.
Sans nods and gets to his feet again. He can almost feel Gaster's disapproving gaze boring into the back of his skull, but he ignores it. Instead, he waves a new shortcut open and steps through, this time to the cave holding the human.
He'll never get used to seeing them like this.
They have their back to a thick, bulky stalagmite, their arms tied to other two on either side, and each ankle anchored to yet more formations separately. Ropes and binds and rags are tied across their entire body, their head, between their jaws, over their fingers, everywhere, leaving little room for anything but shallow breaths. There are still signs of their last attempt at a Reset, spots of blood around their nails and on the rags tied over their palms where they tried desperately to scour their hands open. Sans hates having to keep them like this, but there was no other way to keep them from hurting themself. Even with the thick sweater over their form, it's clear how much weight they're lost, how bony their face is. It's hard to make them eat without purposefully choking on everything.
They're asleep now, thankfully. He doesn't have to see that hateful crimson stare shine out at him like a shower of daggers. He just raises his hand again, and just like before the gems light up, blue envelops the human's chest, and their eyes fly open just as the soul comes whizzing out of their body and stops, quivering, over the skeleton's palm. Like a puppet with severed strings, the human seems to almost die, limbs going slack in their binds, but their eyes stay open, just barely, gaze unfocused and empty, and their breaths turn deep and slow, almost imperceptible.
Just like the subjects Sans used to help the old doc with. But he shakes his head and pushes the thought aside, except that one particular conversation sticks out in his mind.
He remembers Gaster telling him about how the soul always wants to return to its owner, but he'd never fully understood until now. The shining red heart over his hand is vibrating. Its tug on Sans' own soul is stronger than ever, not just because it's fully exposed and so very close, but because he can feel it trying to free itself from the hold of his blue magic, trying in vain to return to the warmth of flesh and blood meant to house it. It almost makes Sans want to close his fingers around it to make sure it won't fly off, but that'd just end in disaster.
Sans uses his other hand to open a shortcut to Gaster. He ignores the old skeleton's look of disappointment. "is the weed still busy?" The former doctor does a head motion that Sans is pretty sure is a sigh, then looks off to the side where he can't see for a moment and nods. "where's alph?" Gaster looks away again, moves one of his hands like he's lazily swatting at a fly, then signs MACHINE at him, which is how he refers to the Extractor without resorting to spelling out the actual name. Sans closes the shortcut without another word.
Another wave of his hand, and the crack reopens, letting him step onto the edge of the pit below the skull-like contraption. "heya," he says, but Alphys rarely jumps at his sudden appearances these days. She just looks over her shoulder and gives him an uncomfortable little 'h-hi' before turning to the hidden panel in the wall. Sans waits patiently, keeping a close eye on the soul. It's resisting less now, but he can still feel it trying to free itself. He won't have to hold it much longer though.
The Extractor hisses on its support as it moves closer, one of its sockets already adapted with the Soul Displacer. There's an empty Soul Pod waiting on the floor too, so once the skull façade of the machine splits open it's easy to put the soul on the pod and slot the whole thing into the socket until a click shows that it's locked in place. Alphys goes back to the control terminal in the wall and taps a few keys to start the extraction. Just like Sans remembers his other self doing, the red heart dissolves into mist tainted by black, and the oily fog is sucked up into the machine and directed down, into the awaiting receptacle at the 'mouth' of the skull.
Except that, unlike last time, the thing receiving Chara's soul is an entirely new pod, built specifically for it and with a very particular shape. Once the extraction is complete, Alphys hurries over to the machine, unlocks the lower receptacle, and brings it over to Sans, but then she stops when her eyes land on the mess of wires across his chest that's part of the Sapphire Enhancer. "Um... M-maybe we should return F-Frisk's soul first?"
The new Soul Pod Alphys is holding, it's shaped in such a way to fit inside Sans' ribcage and stay there, locked in place, hidden and safe from Flowey's spying. And if the Enhancer makes his own soul form in his chest, right where Chara's will be, that's going to be a problem, isn't it? He nods. Alphys is busy holding Chara's pod, so Sans hefts the red one out of the Extractor by himself with a grunt and pulls the soul out. They both move through the shortcut this time, into the human's temporary prison, and Sans lets Frisk's heart loose.
There's a blur of red, and suddenly the kid gasps for air, whole body straining against their bonds until they buckle again, breathing hard for a minute or so. While they recover, Alphys hurries to tear the Enhancer parts off Sans' ribs, fit Chara's pod into his chest, strap its battery to his lumbar, then finish tearing off the rest of the Enhancer mechanism.
It's while the metal parts, broken wires, loose gemstones are cascading onto the hard stone floor that they hear a faint, hoarse noise from Frisk. Both their eyes snap to the human, and finally Sans sees his friend again. There's no malicious red light in their eyes, no tension in their frame, no snarl on their lips around the gag. It's just Frisk, looking up at them, weak, pale, face all sharp bony angles, hair hanging in matted tangles around it. It breaks Sans' metaphorical heart.
The last bit of metal falls off his bones and then he's down on his knees in front of Frisk, pulling the gag out of their mouth, brushing their hair, checking their pulse. It's weak, but stable. "hey kid. good to see ya again. don't worry, i'm sure tori'll have ya back in shape in no time. i'm real sorry about all this."
Frisk says it's okay. They understand. They were watching the whole time. Then, while both Sans and Alphys work on their restraints one by one ("H-hey there," the lizard says when she kneels next to the skeleton), their eyes go to the pod inside Sans' chest, and the ball of swirling black smoke they can just barely make out between his ribs. He glances down too.
"yep. that's your friend," Sans nods without pausing the work of his hands. "gotta keep'em secret until we figure out what to do with them."
Frisk's arms are lowered to their sides, and they wince when the shoulder joints seem to grind full of sand after a long time without movement. Alphys tries to rub some sensation back into them, but that just makes Frisk whimper weakly, so she stops and goes to their hands instead, wiping the crusted blood away, using a bit of healing magic to close the cuts as best as possible. She's not the best at healing, but she can manage little things like this.
Slowly, carefully, Frisk is released from the bonds meant for someone else. They're so weak they can't even stand, Sans has to heft them into his arms, one hand under their knees, the other across their back. They ask about Toriel.
Sans lets out a breath while Alphys sweeps the broken parts of the Enhancer into a shortcut that leads to the magma of Hotland. "yeah, that's not a conversation i'm looking forward to, kid. but we gotta stick to the plan, and she's the best option for getting you back together. me and alph were talking and we got a plan."
Frisk nods to show they're listening.
The shortcut closes, and another opens, bringing them to the room full of beds in the old labs. Sans lays the human on one of them, just for now, and sits on the edge with Alphys on the other side. "so, ya still need to go through the underground the usual way, right? we don't wanna risk changing things more than they already have. so we're gonna bring you back to tori and explain everything to her, and once you're good and healthy again you head out and do things as close to the original plan as possible. while you're recovering me and alph are gonna work on whatever's gonna bring the doc back. i dunno if we'll be done by the time you're good again, we'll give you a new phone to keep in touch. sound good?"
Frisk nods again, but then they want to talk to Gaster.
Sans hesitates, but he opens the shortcut over the bed, and there's the half-molten skeleton, waving at Frisk with a smile. They return the latter, but not the former. And they say they want to do something for Asriel too, not just him.
Only Alphys isn't shocked. "A-Asriel?"
Flowey, Frisk clarifies. Before Alphys can ask more, Sans reaches over and puts a hand on her shoulder. "long story, alph." For a moment it seems like she's going to protest, but she frowns and stays quiet.
Gaster is clearly still taken aback. ARE YOU SURE he signs emphatically, but Frisk just nods. MAYBE NOT POSSIBLE say the hands in the Void, and Frisk understands. NOT KNOW HOW the forgotten skeleton gestures. The human reassures him, says he'll figure it out, they know he can. The Doctor doesn't seem so sure. He looks away, at something they can't see. He wrings his hands again, like wax hot enough to bubble but not enough for the bubbles to break the surface. He looks back at Frisk, at their tired but reassuring smile, looks down at nothing, at his own melded hands, and at Frisk again. WILL TRY he signs. The kid thanks him. He waves them goodbye. The shortcut closes.
Sans can't help but laugh. "yer too determined for your own good, kid."
Frisk just smiles in return.
Then Sans is on his feet again and clacks his palms together. "that's settled then. we'll take care of ya for a bit so you don't look like a corpse when we bring ya to tori, alright? alph, can you get'em started on a bath? im just gonna grab my jacket before i join you."
Alphys shuffles to her feet as well. "Yeah, o-okay. Come on, Frisk."