Chapter Text
The day began as another perfect day at Siloso Beach. The sun hung high in a cloudless sky, its light scattering across the water like shattered glass. Waves rolled lazily onto the shore, leaving behind foamy trails that children chased with squeals of laughter. Colorful umbrellas dotted the sand, and the smell of sunscreen, salt, and fried snacks drifted through the air.
“Don’t go too far!” a mother called, shielding her eyes as her children sprinted toward the water.
“We won’t!” came the reply, already half-lost to the wind.
Out at sea, far enough that the music and chatter of the beach faded into a dull murmur, a lone fishing boat bobbed gently with the tide. The fisherman wiped sweat from his brow and leaned over the railing, muscles straining as he began lowering his net.
“Good weather,” he muttered to himself. “Good day for fishing.”
Below the surface, the ocean was calm.
Schools of fish moved in smooth, shimmering patterns, weaving effortlessly through the water. Sunlight filtered down in pale beams, illuminating coral and drifting debris...
...and then something moved.
The fish froze.
In an instant, their synchronized grace shattered into chaos. They scattered wildly, darting in every direction, panic rippling through the school like a shockwave. Whatever had disturbed them was large. Too large. And it was moving fast.
Without thinking, the fish fled straight into the descending net.
“Eh?” The fisherman blinked as the line suddenly went taut. “Already?”
He grinned, excitement washing away the heat and boredom as he hauled the net back up. Silver bodies thrashed and glittered in the sunlight, packed far more tightly than he’d expected.
“That’s a lucky—”
The words died in his throat.
A shadow stretched across the deck.
Not the thin outline of a bird, nor the shifting shape of a passing cloud.
This shadow was solid. Massive. It swallowed the sunlight whole as it loomed over him, darkening the boat in a way that made his skin prickle.
Slowly, very slowly, he looked up.
Something stared back at him from the water.
It wasn’t a fish. It wasn’t a shark.
Its eyes reflected the sunlight with an eerie, glassy glow. Strange frilled shapes fanned out from the sides of its head, catching the light like translucent sails. Its body was long and sinuous, moving through the water with an unnatural smoothness that made his stomach drop.
The fisherman screamed.
His hands let go of the rope, the net plunging back into the sea along with his catch. He stumbled backward, heart hammering, breath coming in short, panicked gasps.
“No...no, no, no...”
The creature slipped beneath the surface without a splash, its shadow sliding under the boat like a living stain.
The hull rocked once, then twice, and then the shadow was gone—heading straight toward the shore.
Back on the beach, two children knelt in the sand, carefully shaping towers and walls.
“Don’t knock it over!” one protested.
“I’m not!” the other replied. “I’m making the gate!”
Their parents watched nearby, relaxed, half-distracted by their phones and the steady rhythm of the waves.
And then, the water near the shoreline began to churn.
At first, no one noticed.
Then the sea bulged outward.
A dark shape surged up from beneath the waves, water cascading off its body as it dragged itself onto the sand. The frills along its head glimmered in the sunlight, and its eyes locked onto the beach with unsettling focus.
The children looked up.
For a heartbeat, everything was silent.
Then one of them screamed.
People turned. Gasps rippled through the crowd as panic detonated all at once.
“Get back!”
“What is that?!”
“Run!”
The beach erupted into chaos. Towels were abandoned. Sandals were left behind. Parents scooped up their children as people fled in every direction, fear overriding confusion as the creature let out a low, resonant sound that vibrated through the air.
Within moments, Siloso Beach, once bright and lively, was nearly empty, and the Legend of Sentosa was born.
The next morning
Takayama, Japan
The room was dim, curtains half-drawn against the morning sun, and yet the wall opposite Houtarou Oreki’s desk was anything but dull.
Photographs. Newspaper clippings. Handwritten notes, neatly pinned and arranged with quiet precision.
A gallery of monsters that never were.
Houtarou stood with his arms crossed, posture relaxed to the point of laziness, eyes scanning the familiar display. He didn’t need to read the labels anymore. He knew each case by heart.
The Lake Biwa Serpent — proven to be nothing more than tangled eelgrass drifting in low visibility.
The Whispering Shrine Ghost — wind passing through a cracked bamboo wall at just the right angle.
The Hida Yeti — an infamous grainy photograph, ultimately revealed to be the neighbor’s oversized, badly groomed dog caught under a streetlamp.
Urban legends. Cryptids. Myths dismantled one by one.
“Every time I see this,” Eru Chitanda said softly beside him, “I feel like I’m standing in a museum.”
Her violet eyes sparkled with barely restrained excitement as she leaned closer to the wall, fingers hovering just above a yellowed newspaper clipping, careful not to disturb it.
“A museum of solved mysteries,” she added. “But also...unanswered ones.”
“There aren’t any unanswered ones here,” Houtarou replied flatly. “Just misunderstandings.”
Eru hummed, unconvinced.
“But doesn’t that make you curious?” she asked, turning to him with that familiar, dangerous brightness in her gaze. “If these were all explained...what about the ones that haven’t been yet? Somewhere out there, there must be a creature that doesn’t fit into any explanation at all.”
Houtarou sighed, already feeling his energy drain away.
“Curiosity is expensive,” he muttered. “I prefer things that don’t require effort.”
The universe, apparently, disagreed.
The front door slammed open with enough force to rattle the walls.
“GUYS. BIG NEWS.”
Ritsu Tainaka barreled into the house like a runaway percussion solo, shoes barely kicked off before she skidded to a stop. Her grin was wild, eyes practically vibrating with excitement.
Right behind her, Mio Akiyama slipped inside far more carefully, clutching her phone like a lifeline.
“Ritsu, don’t just burst in like that!” Mio hissed, mortified. “Oreki-kun, Chitanda-san, sorry, we should’ve knocked...”
“It’s fine,” Houtarou said lazily. He recognized them instantly.
Even though the two girls attended Sakuragaoka High School, Kamiyama had long been loosely associated with it through shared cultural exchanges and club collaborations. That was how he’d first met Ritsu and Mio—one loud, one quiet, both persistent enough to drag him into conversations he never asked for.
“What’s this ‘big news’?” he asked.
Mio swallowed, then held out her phone.
“We saw this last night. It’s everywhere right now.”
On the screen was a photograph taken at dusk—grainy, shaky, but unmistakable. Something long and jagged cut through the surface of the ocean, its silhouette arcing unnaturally above the waves. Fins glistened faintly, catching the dying light of the sun.
“A sea monster,” Ritsu announced proudly, as if she’d discovered it herself. “Spotted off Siloso Beach, Sentosa. In Singapore.”
“Yesterday evening,” Mio added quickly. “Multiple witnesses. Videos, too—though most of them are blurry.”
She scrolled, showing headlines piling up.
Unknown Creature Spotted Near Popular Resort Beach
Tourists Flee After Shocking Sea Sighting
“It’s already going semi-viral across Asia,” Mio continued, voice tight with worry. “Siloso Beach is one of Singapore’s biggest tourist spots. If this turns into a safety scare, it could seriously hurt their tourism industry.”
Houtarou stared at the image longer than he meant to.
He’d seen dozens like it before. Floating logs. Optical illusions. Clever edits.
And yet...
“This one’s different,” he murmured.
Eru leaned in immediately. “You think so too?”
“I’m not saying it’s real,” he said carefully. “Just...inefficient. If it’s a hoax, it’s an unusually well-crafted one.”
That alone was enough to doom him.
“That means we’re investigating, right?” Eru said, hands clasped, eyes shining.
“...Unfortunately,” Houtarou replied, “yes. For the sake of the country's economy, we'll take on this case”
She clapped once, delighted.
“We’re going to Singapore?!”
Ritsu pumped her fist. “YES! Beach episode! And guess what,” she added, leaning forward conspiratorially. “We’ve got backup.”
Before Houtarou could ask, the door slid open again.
“Wow, Oreki, you haven’t changed at all.”
Houtarou blinked.
“Aoi...?”
Aoi Asahina stood there with her trademark sunny smile, hands behind her back, posture relaxed like she was already on vacation.
They’d known each other for years, long before mysteries, before clubs, before everything got complicated. An old friend. One of the few people who could drag him outside without effort.
“I heard you’re chasing a sea monster,” she said cheerfully. “Thought you might need someone who actually likes swimming.”
Houtarou exhaled slowly.
“...This is turning into a lot of effort.”
And yet, for the first time in a long while, the wall of debunked monsters behind him didn’t feel quite so final.
Somewhere out there, something was waiting.
And whether it was a hoax or not, he was already involved.