Kai Sato's world ended in a haze of rain-slicked concrete and shattered glass. Back in Osaka, it was just another night in the foster trap, Hiroshi's bottle swinging like a pendulum of bad decisions, the old man's slurred "lesson" about stealing scraps from the kitchen. Kai had dodged most of it, fourteen and wiry from too many alley scrambles, but the curb caught him hard. Skull cracked on the edge, blood mixing with puddles, that bottled rage finally boiling over. Not like this, he'd thought, fists clenched even as the black crept in. Not after the orphanage, the scams, the endless "almost families." No sirens, no heroes. Just echoes fading to nothing.
When the nothing cracked open, Kai wasn't on cold stone. He was flat on his back in a stuffy room, staring at a water-stained ceiling. A fan wheezed overhead, stirring air thick with mildew and instant noodle ghosts. His head throbbed, not the skull-split agony, but a dull pulse, like someone had taped a migraine to his temples. "The hell...?" He bolted upright, sheets tangling his legs, and nearly face-planted into a low table cluttered with manga volumes and a half-eaten rice ball. The room was a closet: futon rumpled under him, walls papered in peeling floral, a single window letting in gray dawn light. Sendai? The calendar on the wall screamed it, April 2018, some podunk city he'd only seen on maps.
He staggered to his feet, body feeling wrong. Taller? Buffer? He caught his reflection in a cracked mirror above the sink: same sharp features, black hair a mess of spikes, dark eyes ringed with that perpetual exhaustion. But sixteen now, give or take, shoulders filled out, arms veined from what felt like years of push-ups or street brawls. No scars from Hiroshi's rings, no limp from the orphanage gate slam. "Okay, plot twist," Kai muttered, splashing water on his face. It came out cold, shocking the fog away. "Died and respawned? Or is this some coma fever dream? Hiroshi finally concussed me into anime land?"
No answers from the drip-drip faucet. A crumpled note on the table: Kai, rent Friday. School starts today, don't slack. Love, Ma. Ma? He rifled a backpack by the door, textbooks stamped "Sugisawa High," a navy uniform that fit like it was tailored, wallet with yen and an ID. Kai Sato, 16, local address. No family pics, just echoes of his old hell: the betrayal sting when the foster "siblings" ratted him out for swiping bread, Hiroshi's laugh as the cops hauled him back to the group home. Rage flickered, hot and red in his chest, like a coal someone had jammed under his ribs. He shook it off. "Fresh start, idiot. Act like you belong."
By the time he scarfed a convenience store bento, vague directions kicking in like muscle memory, the streets were waking. Sendai hummed with salarymen shuffling to trains, schoolkids in uniforms chattering about idols and exams. Kai's sneakers, worn but grippy, pounded toward Sugisawa High, the air crisp with cherry blossoms that mocked his inner storm. No monsters in the gutters, no glowing rifts. Just normal. But that pulse in his chest? It itched, like a bruise throbbing under skin. "Chill," he told himself, dodging a bike bell. "You're the new kid, not the haunted one."
Sugisawa squatted like a concrete bunker: gates yawning open, track fields baking under the sun. Kai smoothed his tie, first time it didn't choke like a leash, and slipped into the flow. Whispers trailed: "Transfer?" He kept his head down, alley habits dying hard.
Class 2-3 was controlled chaos. Desks scarred with doodles, teacher, Ms. Hayashi, glasses perched like a hawk, droning about attendance. Kai eased into a back-row seat, backpack thumping. The kid next to him, Yuji Itadori, nametag bold, flashed a grin brighter than the fluorescents. Pink hair spiked wild, eyes lit with that puppy-dog fire. "New guy! Sato, right? I'm Yuji. Track team's desperate, join up? I'll spot you laps."
Kai blinked, caught flat-footed. Old life, "new guy" meant fresh meat. Here? This dude looked like he'd share his lunch with a stray. "Track? Uh, pass. More of a... survival runner." He flexed subtly, his arms had that coiled power, like he'd been throwing hooks in his sleep.
Yuji laughed, loud and zero-filter. "Survival? Sounds epic! Bet I could outrun you anyway, I'm like a human bullet train." He mimed a sprint, nearly toppling his chair. A girl ahead, ponytail sharp as a nail file, twisted around. "Itadori, shut it. Some of us aren't auditioning for circus." But her eyes sparkled, like she lived for the roast.
Kai snorted, tension easing a notch. First semi-smile in... days? "Bullet train with brakes? Bold claim." Yuji barked back, and Ms. Hayashi sighed. "Sato, welcome. Itadori, detention if you corrupt him day one." The class snickered, and Kai sank lower, that red itch quieting to a buzz.
Lunch was roof escape: bento unpacked, city sprawl below like a concrete maze. Kai chewed methodically, mind replaying the alley crack. Died. Respawned. Why? The wind carried chatter from below, kids griping about tests, one muttering, "Heard weird noises last night. Like scratching in the walls." Kai tuned it out. Paranoia central.
Afternoon blurred: math he aced on autopilot, this body's brain was sharper too, PE where Coach barked laps that left him winded but grinning, Yuji trash-talking the whole way. "See? Bullet train!" Kai shot back, "More like derailed cart." They collapsed at the line, Yuji's slap on his back a bro-stamp. "Team tomorrow? Loser buys soda."
"Soda it is," Kai said, the normalcy sinking in like warm rain. Maybe this ain't the trap.
Home was the shoebox again, Ma's note unchanged. Kai heated leftovers, miso soup thin as lies, and crashed early, fan lulling him. Sleep came fitful, dreams of bottles and shadows.
Then the knock.
It started soft: tap-tap, like fingers on wood. Kai jolted awake, clock glowing 2:17 AM. Heart slamming, he froze in the dark. Hiroshi? No, wrong world. The knock repeated, insistent, from the front door. Tap-tap-tap. Not knuckles. Claws? The air turned thick, sour, like rot and old hate. That red pulse roared back, veins burning, a hum vibrating in his teeth.
He crept to the door, fists balled, old instincts overriding sense. Peephole: empty hall, dim bulb flickering. But below the door, shadows pooled wrong, coiling like oil. Another knock, harder, the wood creaking. Something rasped, low and wet. Kai's breath hitched, rage flaring hot. Not again. Not hiding. He yanked the door open a crack.
Nothing. Empty. Then the hall light died, plunging it black. A shape lunged from the gloom, twisted, all limbs and teeth, eyes like burning coals. It reeked of despair, slamming into the frame with a snarl. Kai stumbled back, athletic body kicking in, he swung wild, fist connecting with rubbery hide. The thing recoiled, but slashed, nails raking his arm. Blood welled, hot and real, four furrows tearing down to the bone, muscle parting like wet paper.
Kai hissed through his teeth, pain lancing white-hot, but he didn't scream. He grabbed the doorframe for leverage, new body's strength surging as he drove his knee into the curse's gut. It buckled with a wet crunch, innards shifting under skin like maggots in meat, but the thing didn't fold. It lunged again, jaws unhinging wide, rows of jagged teeth glinting in the faint streetlight spilling from the window. Spittle flew, thick and black, splattering Kai's face, burning like acid on his cheek.
"Fuck you," Kai spat, voice low and ragged, no time for bullshit. He twisted, slamming his elbow into the curse's temple, bone meeting something softer, a squelch as it caved slightly. The thing staggered, but its claws hooked his side, ripping upward in a spray of blood and shirt shreds. Fabric tore, skin split, ribs grinding under the drag. Kai gasped, vision blurring, the red hum exploding in his chest like a furnace kick-starting. Heat flooded his limbs, vision tinting scarlet, strength coiling unnatural, like his muscles were cables under too much voltage.
He didn't question it. Grabbed the curse's arm, twisted hard, heard the snap of tendon, felt it give with a pop. The thing shrieked, a sound like nails on rusted metal, thrashing to free itself. Kai rode the momentum, headbutting its face, forehead cracking against cartilage, blood from his own split brow mixing with the curse's oily ichor. It tasted copper and bile, but he pressed, driving it back into the hall wall with a thud that shook the floor. Fists hammered down, each hit a dull thump into its torso, ribs cracking under knuckles, black fluid oozing from splits in its hide. The curse bucked, claws scraping his thigh, gouging deep, muscle seizing as it tore free a chunk of flesh.
Kai roared, not a battle cry, just raw pain and fury, pinning its arm and stomping down on its knee. Joint gave with a wet grind, leg folding wrong, the thing collapsing in a heap of twitching limbs. It lashed out one last time, teeth grazing his calf, tearing denim and skin in a ragged bite that burned like fire ants. Kai staggered, blood pooling under him, but he stomped again, heel driving into its skull, the crack echoing like eggshell under boot. The curse convulsed, body deflating, dissolving into foul smoke that choked the air.
Kai slumped against the wall, gasping, arm a mangled mess of flaps and bone-glint, side a blooming red ruin, thigh throbbing with every heartbeat. The hum faded, leaving him hollow, sweat mixing with blood in sticky rivers down his skin. Sirens wailed distant, toward school. That pulse again, deeper, calling.
The door hung open, night staring back.