Chapter Text
The snow fell thicker than smoke, muffling the world.
A full moon drowned the sky in pale light. Crickets sang here and there—just enough to keep the night from feeling empty. One called for a mate.
The demon approached in silence. Creatures scattered before him as though he were a storm. His flesh katana clicked softly against its sheath as he walked. His sandals left deep prints in the white plain.
He had a goal. One his mind wished to forget, but his body carried him forward anyway.
The Kamado family. His brother’s close friend. The house that guarded that mockery of a tradition—a breathing style disguised as a god’s harmless dance. A joke.
None of that mattered. What mattered was their death.
Before his eyes touched the cabin, his senses brushed against the presence inside: eight souls. He did not tense. He did not quiet. He remained stoic—the very stillness that made other Upper Moons tremble.
He looked once at the cabin. A humble hut with strings of bells hung around it. He passed through them without pause. Charms against demons, perhaps. Useless.
All he wanted was the people inside.
The door slid open. Eight figures slept in futons: a couple and six children. Kokushibo measured them with a glance. Pathetically weak. His blade slid free without a sound.
On the shelves rested humble tools, well cared for. On the wall hung items of the Hinokami Kagura—the staffs, the robes. Not fear, not admiration stirred in him, but hatred. Yoriichi’s shadow stretched even here.
He turned back to the futons. They breathed softly, peacefully.
Such a shame.
The father stirred first. His eyes flew wide, hand reaching for the axe near his futon. Too slow. Steel whispered. His head struck the floor, blood darkening the wood.
Kie did not wake.
Takeo barely moved.
Hanako’s eyes fluttered open, only to glaze.
Shigeru twitched.
Rokuta never stirred.
Nezuko rose halfway, horror breaking across her face—but before her scream could form, silence cut her down.
Kokushibo raised his blade for the final strike—
The boy’s eyes opened. Dark red. The hanafuda earrings glimmered.
“Father? Mother?”
Kokushibo froze. His six eyes shook. His chest tightened, then stilled. Breath left him in silence.
The boy blinked, noticing the wet stain across his futon. His gaze climbed.
The monster stood above him.
Tanjiro screamed. He scrambled to the corner, eyes darting to the corpses. His throat tore itself raw as he sobbed.
“M-MOM! DAD! SISTERS! BROTH—” His voice broke apart, devoured by grief.
Kokushibo’s gaze stayed locked on the earrings. Hate. Confusion. The kind of turmoil he had not felt in centuries.
His voice, when it came, was cold enough to crush stone.
“Where did you find those?”
Tanjiro wailed louder, flinging anything his hands could reach. The objects struck Kokushibo like feathers. The demon stepped closer, blade slipping back into its sheath. Questions weighed heavier than blood.
“Answer me, boy.” He crouched, towering six eyes boring into Tanjiro’s soul. He studied him like prey—and like a puzzle. Why had Yoriichi chosen this family? Why here?
The boy’s sobs cracked into silence. His throat refused to scream further. Kokushibo raised his katana once more.
And then—
That man.
Muzan’s voice coiled through his mind.
“Kokushibo. Memories of the past still haunt you?”
“I am not haunted, sir. But these earrings—answers linger with them. I believe they may serve our cause.”
“Hmph. Still trembling before his shadow. Very well. Do not kill the boy. Take him. Teach him. If he breaks, discard him.”
“…As you wish.”
Kokushibo struck Tanjiro across the neck. Darkness claimed the boy.
Tanjiro stirred.
The air was cold, heavy with the scent of old incense and damp wood. A thin futon scratched against his skin, rougher than the one at home. His body ached as if he had run for miles.
For a moment, he thought he was back in the cabin. He blinked groggily, expecting to hear his siblings breathing beside him. But the silence was wrong—too wide, too empty.
Then the memories stabbed him.
Blood. His father’s voice cut short. His mother’s stillness. Nezuko’s eyes half-open and empty.
Tanjiro sat up with a gasp, clutching his head. “No… no, no—” His voice cracked, a child’s sob slipping free.
The door slid open.
He flinched. The figure filled the doorway, tall enough to scrape the heavens, eyes too many, too sharp. The monster from his nightmares—no, from reality—was here.
Tanjiro scrambled back, his small hands closing around the nearest thing within reach: a broken broom handle leaning against the wall. He swung it wildly, tears streaking down his face. “Stay away! Stay away from me!”
The demon didn’t move at first. He simply watched, six eyes fixed on him as if Tanjiro were a puzzle he couldn’t quite solve.
The boy charged anyway, his strike clumsy but desperate. The broom cracked in two against the demon’s palm, caught effortlessly.
“You fight,” the monster murmured. His voice was cold, without emotion, yet it pressed against Tanjiro’s chest harder than any blade. “Good. You will need that.”
Tanjiro’s knees buckled, the broken stick dropping from his hands. He couldn’t breathe. Couldn’t cry. The weight of those eyes pinned him to the ground.
The demon crouched, lowering himself until his face hovered close—too close. Tanjiro saw his reflection split in six pupils.
“Remember this, boy,” the demon said. “Weakness is death. If you wish to live, you will learn.”
Tanjiro’s hands trembled. He wanted to scream. To run. To strike. But his body betrayed him, frozen in place as the monster pressed a wooden practice sword into his grip.
“Stand.”
the demon commanded. “You will swing until your arms break, and when they mend, you will swing again. Fight, or die like the rest.”
For a long moment Tanjiro only cried, shoulders shaking. But something deep inside—something his father once taught him about never giving in—forced him to grab the sword with trembling fingers.
His grip was clumsy. His stance, crooked.
The demon’s cold hand shot out and struck his forearm, correcting his hold. The blow stung like fire.
“Again.”
Tanjiro gritted his teeth. He raised the wooden blade and swung.
“Again.”
The sound of wood slicing air filled the shrine, over and over, until his small arms shook with exhaustion. His tears still flowed, but his body obeyed.
The six-eyed demon watched in silence.
He will not break, Kokushibo thought. Perhaps… he can be molded. I think I can see why you chose him, Yoriichi.
Tanjiro grabbed a small pot, close to the shelf and tossed it at Kokushibo's face, his hand struck it and shattered the pot like glass, and Tanjiro managed to hit Kokushibo's knee.
He didn't budge.
His two lower eyes widened slightly.
"And for once you tried something new. Impressive."
Kokushibo’s sandal struck his back. Tanjiro slammed into the floorboards, the air punched from his lungs. He curled on the ground, choking on a sob.
"But I don't want your tricks. I want obedience. Get up and swing the katana again."
That night, the shrine was silent except for the hiss of wind through the cracks.
A small tray sat before Tanjiro: a bowl of rice, a cup of miso, plain and steaming. His hands shook as he clutched the wooden sword still, knuckles rubbed raw. Across from him, Kokushibo sat in silence, tearing his food into neat, mechanical bites.
Tanjiro’s stomach growled, but the boy shoved the bowl aside. “I don’t want it,” he muttered. His voice cracked, heavy with grief. “Not from you.”
Kokushibo did not argue. His six eyes flicked toward the bowl once, then back to his own meal. He ate without a word, without care.
Hours passed. The candle burned low. Tanjiro curled on his futon, staring at the bowl still untouched on the tray. The rice had gone cold, the miso skinning over. His belly cramped and twisted, but shame sealed his throat.
The next morning, the food was gone. The tray was empty, cleaned as if it had never been there. No scolding. No lecture. Just absence. Tanjiro realized too late—hunger was punishment enough.
The days that followed blurred together, one strike after another.
At dawn, Kokushibo forced the boy into stances until his legs quivered. At dusk, he commanded swing after swing until Tanjiro’s arms burned and blistered. When Tanjiro faltered, Kokushibo’s cold hand corrected him with bruising force, smacking his forearm or striking his knee until the posture returned.
The boy’s tears slowed. Not because the pain was less, but because his body had no strength left to waste on crying. His palms hardened, his breathing steadied. He lasted longer each day before collapsing on the shrine floor, his chest heaving like a bellows.
Small scars began to line his skin. The softness of childhood was leaving him, stripped away swing by swing.
Kokushibo watched in silence. No praise. No kindness. Yet he did not stop. He only watched, six eyes unblinking, as the boy stood back up, blade trembling in his hands.
And Tanjiro—though his heart still ached, though nightmares clawed him awake each night—kept swinging.
The young boy slowly lowered the wood katana, and before the demon could hit him, he decided to ask the cruel mentor's name. Not like he'd hope he would answer him.
". . . S-Sir?"
The six-eyed demon turned to his face, no verbal communication was necessary.
"W-What is your name?"
Kokushibo blinked once. For a long, suffocating moment, he gave no answer. His six eyes studied the trembling boy as though weighing something unseen. Then his voice came, low, apathetic.
"Kokushibo."
"T-Tanjiro." He answered, his voice much afraid than his mentor's, but a small hint, a fire that couldn't be explained, that defied Kokushibo's might, even if he knew he was weaker.
Kokushibo's palm slammed on his cheek.
"Swing."
And he did.
The night air carried a new scent. Sour. Hungry. Wrong.
Tanjiro had just finished another round of swings, his hands blistered, arms trembling, when the door to the shrine rattled violently. The wood splintered, and a shadow slipped inside, its eyes burning with hunger.
A demon.
Its gaze snapped to Tanjiro, who froze where he stood, the wooden blade clutched uselessly in his grip. His heartbeat roared in his ears.
The demon grinned, fangs gleaming. “A human… here…”
It lunged.
But before it could take a step further, Kokushibo turned his head. Just his presence—his six eyes glowing faintly in the dark—was enough.
The intruder collapsed to its knees as though crushed under invisible chains. Its claws dug into the floor, its whole body trembling. “U… Upper… One—!”
Tanjiro’s breath caught. For the first time, he realized how demons feared other demons.
Kokushibo didn’t draw his blade. He didn’t need to. His voice alone was a death sentence. “Leave. Or be gone.”
The demon’s body disintegrated in a frenzy of terror, tearing itself apart as it fled into the night.
Tanjiro stood trembling, the wooden sword slipping from his grip.
The shrine door rattled again—this time not with fear, but with force. A figure stepped inside, upright, broad-shouldered, tattoos curling across his skin.
Akaza.
“Oi, Kokushibo,” he called casually, his voice sharp with annoyance. “You’ve been hiding. What are you doing wasting time in a rotten shack?”
Kokushibo didn’t move. “Leave, Akaza.”
Akaza’s eyes flicked to Tanjiro, who had scrambled back, clutching his wooden blade again. His lips curled. “What’s this? A human? Don’t tell me you’re… babysitting.”
Tanjiro, shaking but defiant, swung the practice sword at him. “Stay away!”
Akaza didn’t even blink. His fist shot out almost like a bullet, stopping just short of shattering the boy’s skull. The air cracked with the force. Tanjiro crumpled, the sword knocked aside.
“Pathetic,” Akaza spat. “You’re wasting your time.”
For the first time in centuries, Kokushibo’s composure cracked. Veins bulged along his temples, his aura flaring like a storm. The walls of the shrine quivered, the air itself trembling under his killing intent.
Akaza stepped back, bristling. “Tch—so it’s true. You’re protecting him.”
Kokushibo’s voice was low, dangerous. “Leave, or I will cut you into pieces so small Muzan himself will not find them.”
The two demons locked eyes, the silence heavier than steel. Then Akaza scoffed, stepping back toward the door. “Do as you like, Kokushibo. Just don’t come crying when that weakling slows you down.”
He vanished into the night.
Tanjiro lay trembling, staring up at Kokushibo in shock. Not at Akaza’s violence, but at the fury he had seen in Kokushibo’s eyes—fury not aimed at him, but for him.
Days bled into weeks.
Tanjiro’s body grew harder, faster. The boy who once collapsed after ten swings could now last until his arms bled. The child who sobbed at every bruise now gritted his teeth, pushing himself to stand even when his vision blurred.
Kokushibo gave no praise. Only more corrections. More scars. More drills.
The shrine became a forge, and Tanjiro the blade beaten within it.
When his twelfth year came, Kokushibo set a new task before him: combat against real demons. No more practice. No more excuses. Only life or death.