Tsutsumi stood atop the speeding Mugen Train, the night wind howling past him. Sparks of friction flared along the metal roof as his boots pressed down, steady and deliberate.
Across from him, the demon trembled, pale face twisted in fear.
Tsutsumi's eyes narrowed. He began walking forward, slow, unhurried steps echoing over the thunder of the rails.
The demon's nerve broke. He turned and bolted.
Final Attack Ride: O-O-O-OOO!
Three glowing rings appeared in the air ahead, yellow, red, yellow, each pulsing with raw energy.
Tsutsumi broke into a sprint.
He passed through the first yellow ring, his lion headpiece blazing to life, sunlight refracting off the metal and scattering gold light across the night.
He stepped into the second ring, crimson flames enveloping his body, their heat roaring like a furnace.
Through the final yellow ring, his speed surged beyond human sight.
The next instant, he struck.
The impact tore through the air, hurling the demon upward like a ragdoll. Tsutsumi's arm shot out, fingers seizing the demon's hair mid-flight. The creature screamed as fire and reflected sunlight burned through its skin.
Without a word, Tsutsumi leapt from the train, landing in stride upon the ground below.
Still gripping the demon, he dragged it along the dirt, its body grinding through gravel and soil, smashing through trees with deafening cracks. Flames and embers scattered behind them, a blazing scar across the forest floor.
Less than a minute later, it was over.
The demon's screams faded into silence. What little remained of him crumbled into ash, scattering in the cold night air.
Tsutsumi finally stopped, breathing steady. His clothes shifted, leaving him once more in his black train driver's uniform.
He turned his gaze back toward the tracks. The Mugen Train, gleaming in the moonlight, was approaching again, its wheels screaming softly against the rails.
As it passed, Tsutsumi raised one hand and caught the edge of the car with effortless grace. He let the motion pull him in, his body disappearing into the night as the train carried him onward.
Stepping back into the train, Tsutsumi moved through the narrow corridor toward the passenger section, checking if there was anything left to deal with.
The moment he slid the door open, he froze.
A boy wearing a green-and-black checkered haori stood in front of a small demon girl dressed in pink. Her hands were burning with pink flames, and she pressed it onto the other passengers.
Tsutsumi stared for a long moment.
"Another crazy one…" he muttered, placing a card into his belt.
"Henshin."
Kamen Ride: Hibiki!
Purple fire erupted, swallowing his form. When the flames dispersed, his uniform remained, but his skin had turned a deep blue, and two metal horns jutted from his head.
The boy's eyes widened in shock.
"A demon!?" He stepped forward, pushing the girl behind him. "Stay back, Nezuko!"
Tsutsumi said nothing. He simply reached behind his back and drew the Ongekibou Rekka, gripping one drumstick in each hand.
The boy lunged first. His blade flashed, cutting through the air in a whirl of blue light.
"Water Breathing: First Form: Water Surface Slash!"
A wave of water burst from his swing, rushing toward Tsutsumi's neck.
Tsutsumi raised one Ongekibou to parry, the metallic crack echoing through the train car. His other hand slipped a card into his belt.
Attack Ride: Onibi!
He inhaled and exhaled a breath of violet flame.
The blast engulfed the swordsman, the heat searing his skin. The boy grunted in pain, slammed back by the force of the flames.
Tsutsumi followed with a powerful swing, sending the boy crashing against the far wall.
The demon girl lunged at Tsutsumi, claws extended.
Attack Ride: Onizume!
Their claws collided midair, sparks and embers bursting from the impact. Nezuko was thrown back, slamming into the wooden wall hard enough to crack it. She cried out, clutching her bleeding hand.
Before Tsutsumi could finish her off, another voice cut through the chaos:
"Lightning Breathing: First Form: Thunderclap and Flash!"
A blur of yellow light shot forward.
Tsutsumi barely turned before the sleeping blonde boy streaked past like lightning, his katana carving through the air.
The strike hit dead-on, sending Tsutsumi crashing out through the side of the train. His claws dug into the metal plating, screeching as he slid along the exterior, leaving deep grooves in the steel.
He gritted his teeth. "...Motherfucker."
With a powerful push, he flung himself back onto the roof. Wind roared past as he steadied his stance, looking down through the roof's torn panel.
He'd been caught off guard, not by the strength of the attack, but by the fact that the boy was still asleep.
"This world keeps getting weirder," he muttered under his breath.
He flexed his hand, noticing the deep slash across his palm slowly knitting itself shut. The blue flesh shimmered faintly as his oni physiology accelerated the healing.
Within moments, the wound was gone. He wiped away the blood and glanced back toward the train interior.
Attack Ride: Electrification!
Magenta lightning surged across Tsutsumi's body, his hair spiking upward as arcs of electricity danced through the air. His skin glowed with a faint magenta hue, the static crackling like an angry storm.
He moved in a blur. In a heartbeat, he appeared behind the wounded demon and flung open the door just as the two boys noticed him.
Attack Ride: Polarity!
Tsutsumi raised his hand lazily to the side.
Both swords flew from the boys' grips as if yanked by invisible chains, the katanas slamming into the metal wall with a ringing clang. Then, pieces of the train itself twisted free, metal plates warping and snaking around their bodies, pinning them hard against the wall.
Nezuko looked up at the sight, eyes wide, but before she could move, Tsutsumi kicked her away. She tumbled across the floor, gasping as he advanced with deliberate steps.
"Wait! Please! Don't hurt her!" the boy in green shouted, his voice breaking with desperation.
Final Attack Ride: Hi-Hi-Hi-Hibiki!
The Ongekiko drum flew from Tsutsumi's belt, glowing ominously. Instead of fleeing, Nezuko ran toward her brother, spreading her arms wide in front of them. The drum device locked onto her chest before expanding.
"NEZUKO!!" the boy screamed.
Tsutsumi kept walking, unbothered. He raised his Ongekibou Rekka high, ready to bring it down.
A blade caught the strike mid-swing, steel shrieking against steel.
Standing between him and Nezuko was a man with long, bright yellow and red hair, his eyes blazing with conviction.
"Move," Tsutsumi said coldly.
"Please, Mister Hibiki!" the man said, pushing back and lowering his blade. Then, to Tsutsumi's surprise, he cast the sword aside entirely. "Nezuko is a special case! She's a demon, but one who still holds her humanity! Please, don't kill her!"
He dropped into a ninety-degree bow, his voice echoing through the rattling train.
Tsutsumi paused, watching him in silence. The man's posture, his unarmed stance, it wasn't a trick. It was an act of pure, desperate trust.
The man straightened, drawing a deep breath. "I am Rengoku Kyojuro, the Flame Hashira of the Demon Slayer Corps! I swear, on my title and honor as the Flame Hashira. Please, spare her!"
The air fell still. Even Tsutsumi hesitated, reading the sincerity in Rengoku's voice. The way he said Hibiki told him this man had some faint connection, or at least respect, for the oni warrior he had invoked.
Finally, Tsutsumi lowered his weapon.
Before anyone could speak again, a deafening explosion ripped through the front of the train.
The floor trembled as the blast spread in a chain reaction.
Attack Ride: Connect!
A massive magenta circle flared beneath Tsutsumi's feet, expanding through the entire train car. Light swallowed all the passengers on the train.
When the glow faded, they were all standing on solid ground under the cold night sky.
Rengoku, the boy, Nezuko, and all of them looked around in confusion. Behind them were the still passed-out passengers, in front of them, the wreckage of the Mugen Train burned in the distance.
Tsutsumi exhaled slowly, eyes narrowing. His train was destroyed.
"My train..." Tsutsumi said through gritted teeth.
He wasn't happy.
A voice cut through the crackle of fire. "How were you able to do that?"
From the wreckage stepped a pale-skinned demon, his body marked with blue stripes. His eyes locked on Tsutsumi.
Tsutsumi didn't reply. His fury simmered beneath his calm expression. He simply reached for another card.
Final Kamen Ride: Hibiki! Armed!
Crimson flames roared to life around him, wrapping his body in spiraling light. When the fire cleared, his oni skin turned crimson, with his horns spreading into fours.
He drew his Rider Book blade and slotted in one last card.
The striped demon smirked and charged.
Final Attack Ride: Hi-Hi-Hi-Hibiki!
The ground split apart beneath them. Tsutsumi's blade ignited, releasing a pillar of magenta flame that pierced the sky like a beacon.
The demon's smirk twisted into panic. He tried to dodge, but the strike had already landed.
The blast consumed him.
When the fire finally died, only a charred hand and two scorched feet remained.
Tsutsumi exhaled, letting his transformation fade. He turned back into human form.
He glanced at the burning wreckage of his train, muttering under his breath, "...How annoying."
Without another word, he turned and walked toward the nearby forest. His figure blurred into the shadows before vanishing entirely, the Aurora Curtain swallowing him whole as he departed this world.
Returning to his own world, Tsutsumi headed straight home. The place was quiet, too quiet. Miyu wasn't there.
He frowned slightly before making his way to Jiro's house. There, he found her sitting on the porch, leaning on the suitcase.
"My parents took Miyu on vacation to Kyoto," she said casually, standing and walking into his house. She dropped her suitcase beside the sofa and flopped down with a sigh, sinking into the cushions.
"You're right," she muttered, staring blankly at the ceiling. "This really is a shitty vacation."
Tsutsumi came out of the kitchen holding a plate of fruit. He sat beside her, bit into an apple, and turned on the TV, still annoyed about the earlier incident in the other world.
"Feed me," Jiro said, opening her mouth without looking at him.
He sighed but humored her anyway, picking up a blueberry and dropping it into her mouth.
The two lounged lazily under a light blanket, the TV flickering across their faces.
"We're out of snacks," Jiro complained, stretching and resting her legs across his lap.
"There should be some chip bags in the food closet," Tsutsumi replied. "Bought them for Miyu, she gets one every now and then."
"Can you get it? I'm too comfortable to move."
"Can't. Your legs are on me."
"I don't want to move. You're warm."
"Then how am I supposed to get up?"
"Not my problem."
Their small back-and-forth filled the quiet room, half teasing, half genuine laziness, until something soft thumped onto the table in front of them.
Both looked over.
A small, round creature, black and red, with two floppy bunny ears and a glowing digital face, stood there, holding two chip bags in its tiny hands before it placed them on the table.
"Thanks," Jiro said automatically, grabbing one of the bags. Then she froze mid-bite, chips halfway to her mouth.
Tsutsumi blinked. Something definitely felt off.
They both turned toward the creature, which tilted its head curiously at them.
"…What is that?" Jiro asked, eyebrows raised. "It's… kinda cute?"
Tsutsumi narrowed his eyes. "How did a Bangboo even get here…?"
He remembered copying the data and blueprints of one back in that other world, but he definitely hadn't built one.
Jiro poked the creature's side. "It feels soft, like fur… but it's mechanical underneath. Did you make it in your off time or something?"
He opened his mouth to say no, then froze.
His long coat and shirt, made entirely of micro-robotic grasshoppers, were missing from where they hung on the wall.
"…I don't remember giving you permission," Tsutsumi said flatly, addressing the Bangboo.
The little creature straightened and flapped its ears.
"Mm-hmm! Mm-mm-hmm! Mm-mm-hmmm!" (But Boss, it was boring being hung up collecting dust! I wanted to help!)
Somehow, Tsutsumi understood every word.
"A bit unnecessary," he said, "but sure."
The Bangboo's ears perked up happily.
"Got a name, or do you want me to name you?"
"Mm-hmm! Mm-mm-hmm!" (Please name me, Boss!)
"Then you'll be Azu."
The Bangboo, now Azu, jumped excitedly, little feet tapping against the floor before it ran off down the hallway, humming digital noises to itself.
Tsutsumi leaned back into the sofa.
"What?" he asked, noticing Jiro's bewildered stare.
"Do you actually understand what that thing's saying," she asked slowly, "or are you just screwing with me?"
"Yes," he answered simply.
Jiro squinted, then kicked him lightly in the side. "Asshole."
She huffed, threw a chip at him, and settled back down. The TV kept flickering, the house quiet again, save for the soft mechanical humming of Azu somewhere in the kitchen, already making itself at home.