The air in the Infinity Castle pulsed with a quiet, eerie hum, broken only by the distant echo of footsteps and the occasional annoyed growl.

Muzan Kibutsuji stood tall in the shadows, arms crossed, his expression unreadable as crimson eyes followed the chaotic trail left by his young son—his heir—darting between the legs of the Upper Moons like a mischievous wraith.

“...He’s fast,” Muzan murmured to himself, watching the blur of claws, giggles, and tiny horns weaving past Akaza’s leg just before the martial demon lost his balance for the third time that evening.

“Stop. Moving!” Akaza barked, trying to catch the child, his jaw clenched with rising irritation. “Lord Muzan, your son is—”

“Thriving.” Muzan’s tone was soft but final. “Let him be.”

Doma, as expected, was all smiles, crouching to open his arms wide. “Come here, little monster! I have candied eyeballs~!”

The child barreled toward him—and then turned last second to yank the collar of Doma’s robes and sprint the other way, laughing like a banshee. The fabric ripped clean off one shoulder.

“RUDE~!” Doma sang, spinning in a circle with mock offense. “He gets it from you, Lord Muzan.”

“Of course,” Muzan replied dryly. “He is mine.”

“Get back here!” Kokushibo growled, his blade still unsheathed from the last attempt to discipline the child after being tripped—again—by a tail whip. “He is a distraction.”

Muzan’s gaze turned slowly to him. “You are the Upper Rank One. And yet my infant distracts you? Disappointing.”

Kokushibo’s eye twitched. “...My apologies.”

Kaigaku muttered curses under his breath from the corner, hiding behind a pillar as the boy stalked him like a predator.

“You were bragging last week about how you could crush a Hashira in seconds,” Muzan said lazily. “Now, you’re hiding from my son.”

“I’m strategizing,” Kaigaku shot back, immediately ducking as the child hurled a severed doll head with inhuman strength at his face. It exploded against the wall, embedding teeth in the stone.

Muzan's lips twitched in what might've been the beginnings of a smile.

“Gyokko,” he called without turning.

From a swirled vase nearby, Gyokko’s distorted face emerged. “Yes, Lord Muzan?”

“Why do you have my son’s horns growing out of your neck?”

Gyokko screamed. “I didn’t do this! He stabbed me with his baby claws and left them there! They’re—growing—on their own!”

Behind him, the demon child cackled like a mad hyena and somersaulted through a portal made by Nakime, who sighed, her biwa strumming just fast enough to keep him contained to one room.

“Lord Muzan… may I confine the boy to a spatial loop?” she asked, visibly trembling.

“No,” Muzan replied. “He needs freedom to hunt.”

Crash!

A bloody vase shattered against the floor, the shards reassembling just to shatter again as the demon child passed by, shrieking with glee and tackling Hantengu to the ground.

“I am so scared!!” Hantengu cried, rolling in panic. “H-He licked me again!! He knows my fears!!”

Zohakuten appeared beside him with a snarl. “Control him, Muzan-sama! Or I will—!”

“You will what?” Muzan asked, stepping forward just slightly. His presence silenced the room in an instant.

Zohakuten clenched his jaw and backed down. Muzan’s voice was colder now. “He is my legacy. My blood flows in his veins. His instincts are those of a superior predator. You should be honored he even notices your existence.”

The demon child, eyes glowing a deep amethyst, scuttled up Muzan’s back like a bat and perched on his shoulder, whispering something unintelligible but wild with glee. Muzan’s expression softened for the first time in centuries.

“See?” he said. “He favors me most.”

“Of course he does,” Doma muttered, cradling his now half-eaten wig. “You’re the only one who hasn’t been headbutted yet.”

“I would not be,” Muzan replied simply, lifting his hand to let the boy balance on his arm like a falcon.

The child blinked—then bared tiny fangs and lunged at Akaza again, tail wagging like a delighted wolf.

BOOM.

Akaza flew through three wooden beams before disappearing into the void. Doma clapped.