The Infinite Castle: The Sound of the Biwa
Following Hakuji's plan, Gyutaro advanced deeper into the Infinite Castle. Just as he was about to reach the same area as before, a clear biwa note rang out — exactly as expected.
In an instant, the space around him twisted and reconfigured at blinding speed. The scenery blurred — and the next moment, Gyutaro found himself standing beside Akaza once again.
Hakuji, whose eyes had been closed within his Compass Needle's field, suddenly opened them wide.
"Gyutaro! Southeast direction — directly above us!"
At once, both demons gathered power into their legs and launched forward, bursting toward Nakime's position at terrifying speed.
But Nakime remained calm and unshaken. The single eye beneath her bangs opened slightly, and a faint, disdainful smile curved her lips. Her fingers began to pluck the strings of her biwa — a sharp, vigorous melody that echoed through the endless halls.
The Infinite Castle responded instantly. The layout of the space began to change with every note she played. Floors, ceilings, and walls twisted and folded like the pieces of a living puzzle.
Hakuji and Gyutaro found themselves rising and falling through space, their positions shifting constantly as the music played on.
When the last note rang out, the two demons — after all that movement — once again stood right back at their starting point.
Gyutaro snarled in frustration, clawing at his face.
"Damn it! Even if we can sense her location, the distance is too great! Before we can reach her, she just sends us straight back to the beginning!"
The Battle Outside
Meanwhile, outside the Infinite Castle, the situation on the battlefield was growing dire.
Even with the Demon Slayer Corps' strongest fighters — the Hashira, the Butterfly Sisters, and allies like Koyuki, Ume, and Michikatsu Tsugikuni — they could not even break through Doma's and Hantengu's attack ranges, let alone challenge Muzan Kibutsuji, who had yet to move at all.
The tide of battle was entirely under Muzan's control.
"Hinokami Kagura — Setting Sun Transformation!"
"Thunder Breathing, First Form: Thunderclap and Flash — Sixfold!"
Tanjiro leapt high into the air, flipping upside down as he swung his blade in a blazing horizontal arc, flames swirling around him. His strike shattered half of the ice maidens Doma had just summoned.
Zenitsu followed up immediately, slicing through the remaining half.
But Doma only smirked. The ice maidens were mere constructs of his Blood Demon Art — their destruction meant nothing to him.
"Blood Demon Art: Rime – Water Lily Bodhisattva!"
He spread his fans, conjuring a colossal ice bodhisattva with hands clasped in prayer. The towering figure rose at the center of the battlefield, then brought down its hands like blades, cleaving the ground toward the Demon Slayers.
Sensing the immense power behind the attack, everyone scattered to avoid the blows. But retreating only opened them up to further danger.
"Blood Demon Art: Infernal Wooden Prison!"
Zohakuten struck the twin drums on his back, summoning countless massive wooden dragons that coiled and writhed through the air, surging toward the group.
"Everyone, behind me!" shouted Tengen Uzui.
"Sound Breathing, Fourth Form: Violent Rain!"
Uzui spun his chained dual blades in wide, explosive arcs. Each strike detonated with a deafening blast, meeting the wooden dragons head-on and holding them at bay.
But Doma's ice bodhisattva attacked again — from its mouth spewed a stream of ice crystals laced with deadly poison, capable of freezing human flesh solid.
"Wind Breathing, Fourth Form: Rising Dust Whirlwind!"
Sanemi Shinazugawa slashed upward, sending a storm of wind blades spiraling skyward to block the oncoming frost.
Just as the attack was repelled, a quiet voice spoke — and time seemed to still.
"Word Command: Force."
Muzan Kibutsuji had finally made his move.
An immense, invisible pressure crashed down on Sanemi, crushing him under a gravitational force so heavy that it broke his stance mid-form. His concentration shattered — and the ice crystals swept forward once again.
Seeing Muzan act, Kokushibo and Muichiro instantly stepped forward to shield the others. In perfect harmony, they intercepted the freezing blast and created an opening for counterattack.
"Moon Breathing, Tenth Form: Endless Moons!"
Both slashed simultaneously, unleashing massive overlapping arcs of moonlight that spiraled outward in a storm of crescent blades.
The spreading ice and wooden dragons were obliterated in an instant, scattering into shards — the chance to counterattack had come.
"Now!" Michikatsu roared. "Before they reform — attack!"
But just as the Demon Slayers began their offensive, Muzan's cold laughter filled the air.
"Do ants believe they can shake a great tree? Word Command: Instant."
In a blur, Muzan appeared directly before them. Their blades were already mid-swing when he raised one pale hand.
"Word Command: Repel."
A tremendous, unseen shockwave burst outward, deflecting every attack and sending the Demon Slayers flying.
With a single move, Muzan had entered the battle — and in mere moments, every combatant was injured.
"So these are humanity's strongest demon slayers? Pathetic. I truly can't fathom how the Twelve Kizuki I created ever failed to annihilate you. But it matters little — you'll all die soon enough, so I see no point in pondering it further."
The tendrils on Muzan's body lashed outward like whips, stabbing toward everyone simultaneously.
The slayers fought desperately to defend themselves — now forced to guard against not only Muzan's relentless onslaught but also the opportunistic strikes from Doma and Hantengu. The tide of battle had turned entirely against them.
Within the Black Coffin
Inside the Black Coffin realm, Yosuke's missing heart had fully regenerated. Yet he still could not make contact with the System, nor sense what was happening outside.
The Priest Master's voice echoed around him.
"Yosuke Ubuyashiki, perhaps you should be more concerned about your comrades. Truly, our only conflict is this: I seek to restore order, while you sow chaos. You may believe you're saving everyone, but in the end — you'll save no one."
"Out of respect for the bond between us, I'll grant you a chance — a chance to return everything to the correct path. Hand over the Power of Law within you. Let those who are destined to die meet their end, and step aside. Do this, and I shall dissolve my alliance with Muzan Kibutsuji. Muzan will perish according to the fate that was originally written."
The Priest Master's tone was calm — but his words carried the weight of final judgment.
Yosuke's expression hardened. He saw through the lie immediately.
"So that's it. All of this… you're after the Power of Law inside me."
"Let me guess — you're an agent of fate. You act in its name, but you're still an independent being. And as long as you're separate from fate itself, you possess your own thoughts… your own will."
"Your cooperation with Muzan was mandated by fate — a means to restore the destined timeline. But now, you're trying to strike a deal with me. That means you want to break free from fate's control. And the complete Power of Law within me… that's your key to freedom. Am I wrong?"
The Priest Master's expression darkened.
"No wonder humans say wisdom comes with age. You see through everything, don't you?"
Yosuke gave a cold, sharp laugh.
"Takes one to know one."
"So, you refuse to cooperate… Very well. I'll take it myself."
"I've already deciphered this Black Coffin's structure. Let the outcome be decided — not by words, but by battle. Outside, in the real world."
As the Priest Master's voice faded, cracks began to spread across the dark realm. From within the fissures, blinding light spilled through, piercing the endless blackness.