The Flame Hashira, Rengoku Kyojuro, and the Sound Hashira, Tengen Uzui, ran through the twisting corridors of the Infinity Castle.
Floors folded into walls. Corridors bent at impossible angles, tilting and warping as if reality itself was being rearranged mid-stride. Yet neither of them slowed. They leapt across sudden gaps, slid along slanted beams, and adjusted instantly to every spatial distortion, as if the castle itself dared them to fall behind.
"Upper Rank Two is down," Tengen said as they ran. "Upper Rank Three as well."
Rengoku's eyes burned with unwavering resolve. "Then all that remains is Kibutsuji Muzan! But we still don't know whether he's alive or dead."
Tengen let out a grim grin.
"The crows said Akira suddenly turned into a wolf and beat him, but they never confirmed Muzan's death. And if Muzan really died, all demons should've vanished with him. This place still exists, and demons are still running around."
He clicked his tongue.
"So yeah. He's probably still alive."
Rengoku nodded once.
"I see. Then the final battle isn't over… yet."
Tengen laughed sharply.
"Good. Then we just need to give it a flashy ending."
They landed on a broad platform.
And suddenly, a sound cut through the castle.
A scream.
"Don't! Don't kill me! Muzan-sama, please!"
Both Hashira froze.
Rengoku turned sharply toward the echoing cry.
"That direction!"
They sprinted again, racing through a warped passageway that twisted unnaturally before opening into a massive chamber.
And there.
At the center of the space lay something wrong.
A grotesque monstrosity sprawled across the floor like a living tumor. It had no true shape, only layers of muscle, bone, and sinew fused together in a swollen mass of flesh. Its body resembled a gigantic, bloated slug, glistening wetly as it dragged itself forward using two enormous arms that crushed the stone floor beneath them.
From all over its body sprouted countless flesh tentacles, writhing and coiling like living whips.
And at the front.
A face.
Muzan's face.
Distorted, warped, yet unmistakably his. From that face came an unintelligent, monstrous sound, devoid of reason.
One of his flesh tentacles held a demon half-absorbed into the mass. The demon screamed in pure terror.
"Please… please don't…! I'll be useful! I won't fail again!"
The creature did not listen.
A mouth opened.
No, not his mouth. The flesh itself split far beyond any natural limit and swallowed the demon whole.
As it did, the mass expanded.
His muscle swelled. Tentacles multiplied. The floor groaned under the increased weight.
Tengen's grin vanished.
"…That's not flashy at all."
Rengoku stepped forward, his hand tightening around the hilt of his sword, flames flickering faintly in his eyes.
"So this… is his true form."
The grotesque body shifted.
Muzan's distorted face turned toward them.
And his eyes locked onto theirs.
The moment Muzan turned toward them, the Infinity Castle itself seemed to recoil.
Rengoku moved first.
"Flame Breathing — First Form: Unknowing Fire!"
His body surged forward at tremendous speed as he unleashed a singular horizontal slash aimed straight at Muzan's core.
But before his blade could reach its target, Muzan's tentacles shot out.
They blocked the strike instantly.
More tentacles followed, lashing out at the same time. One pierced through Rengoku's guard and struck him directly, slamming him into the floor with crushing force.
"Gah…!"
Stone shattered beneath him.
Tengen followed in a blur of motion.
"Sound Breathing — Fourth Form: Constant Resounding Slashes!"
His dual blades struck in rapid succession, explosions chaining together as detonations ripped through Muzan's tentacles. Chunks of flesh were blasted apart, shockwaves roaring through the chamber and rattling the warped walls.
For a heartbeat.
It looked like it worked.
Then the flesh twisted.
The torn tentacles regenerated instantly, knitting back together as if nothing had happened.
Then Muzan moved.
His massive body surged forward with impossible speed.
Tentacles lashed out like spears, dozens at once, slicing through the air faster than the eye could track. Rengoku barely twisted aside, a tentacle grazing his shoulder and tearing through muscle as if it were paper.
"Gah!"
Tengen blocked another strike, but the sheer impact sent him skidding across the floor, boots carving sparks as he crashed through a pillar.
"…Fast," Tengen muttered, forcing himself upright.
"Way too fast for something that ugly."
Rengoku planted his sword into the ground, breathing hard, but still smiling fiercely.
"Then we'll burn brighter!"
They attacked again.
Fire and explosions collided with writhing flesh, blades, and detonations, tearing into Muzan's body.
But Muzan adapted instantly.
His wounds healed in an instant, and his tentacles struck like a storm.
Rengoku was hit midair, slammed into the floor so hard the stone beneath him exploded apart.
Tengen intercepted a killing blow meant for him, but the force snapped him back, blood spraying from his mouth as he was hurled away.
Then Muzan's body opened.
Mouths split across his torso, arms, and back, all over his grotesque form.
A thunderous shockwave erupted.
The blast crushed the air from their lungs and hurled both Hashira violently across the chamber.
Rengoku hit the ground hard.
Tengen rolled, barely stopping himself from falling into a collapsing gap.
Both of them lay wounded.
Blood dripped from their injuries as they struggled to breathe. Muscles screamed. Their bodies refused to rise, no matter how hard they tried.
They were too weak.
And above them.
Muzan loomed.
A forest of tentacles rose into the air.
Ready to strike the finishing blow.
Just as the forest of tentacles descended.
Two figures rushed past them.
Six swords spun at once, rotating like bladed storms as they intercepted the attack head-on. Steel clashed against writhing flesh, sparks and shredded sinew flying as the tentacles were blocked inches away from the fallen Hashira.
They were Yoriichi-Type Null Units.
Tengen's eyes widened. "Oh, those are…"
Then he noticed something else.
Tatami doors.
Not one.
Dozens.
Across the walls, the ceiling, the floor, every surface of the massive chamber, tatami doors slammed open one after another.
Figures stepped through.
"Did we keep you waiting?" Mitsuri said brightly as she emerged, her expression fierce despite her smile.
Obanai appeared beside her, followed by Giyu and Tanjiro.
From another door, Shinobu, Zenitsu, Inosuke, Kanao, and Alpha stepped through as well.
Another door opened, and Sanemi, Gyomei, Muichiro, and Genya appeared.
More doors followed, releasing additional Demon Slayers and the remaining Type Null Units, until the chamber was filled with allies.
Finally.
Another door slid open.
Akira stepped through, followed closely by Erika, who looked visibly exhausted as she walked behind him.
Akira glanced around, then let out a breath of relief.
"Looks like everyone here. Good thing Yushiro finally learned how to control this thing."
Then his gaze lifted.
He stared at Muzan's grotesque form.
"…Oh my god," Akira muttered. "Is that Nurgle the Plague Lord?"
Erika followed his line of sight, blinking tiredly.
"Is that Muzan…? What happened to him?"
Muzan answered first.
The instant he saw them all gathered together, his entire mass convulsed, and every tentacle launched forward at once.
A storm of flesh and bone surged toward the group.
Before anyone else could react, all ten Type Null Units leapt forward in unison.
Their six blades spun violently, forming whirling shields of steel as they blocked every incoming tentacle. Flesh was shredded, strikes deflected, the impact echoing through the chamber as the Null Units held the line.
Behind them, the Demon Slayers raised their weapons.
The final battle was about to begin.
With Muzan's initial assault blocked and countered by the Type Null Units, everyone moved at once.
The spinning blades of the Null Units carved through incoming tentacles, steel screaming as flesh was shredded apart, but even so, they were slowly being pushed back. Muzan's tentacles regenerated as fast as they were cut, multiplying, pressing forward with overwhelming numbers.
Seeing this, the Demon Slayers charged in.
Nichirin blades flashed as they attacked from every angle, slashing at tentacles, severing joints, burning flesh. But Muzan responded instantly, his tentacles lashed out at terrifying speed, striking back in every direction.
Even though the Demon Slayers had been trained by Akira specifically to deal with attacks like this, Muzan now had far too many tentacles.
They began to get overwhelmed.
The Type Null Units shifted formation immediately, stepping in front of the Demon Slayers, intercepting strikes meant to kill. Blades spun faster, bodies moved with mechanical precision, buying precious seconds.
Together, Type Null Units and Demon Slayers fighting side by side, they managed to stay alive.
Still, no matter how many times they struck.
Muzan healed instantly.
Tentacles regrew without pause. Flesh reformed. His attacks never slowed.
Tanjiro gritted his teeth as he fought, breath ragged.
"Why does Muzan look like this…? How is he this strong?!"
Akira, watching closely, answered calmly.
"Well… he must've drunk those blue potions I created."
Rengoku and Tengen, who had just finished drinking the same blue potion to heal themselves, turned their heads sharply toward him.
"…What?" Tengen said flatly.
Tanjiro stared.
"I thought those blue potions only healed injuries."
Akira nodded.
"They do. They contain modified wisteria extracts. If a human drinks them, they heal. If a demon drinks them…"
He paused.
"They heal, too. But they also get stronger."
Sanemi snapped instantly.
"ARE YOU NUTS?! Then why did you make all of us carry them?!"
Obanai followed, eyes sharp.
"Yeah. If a demon gets their hands on them, wouldn't they just grow stronger?"
Even Erika shot Akira a look that clearly said: Don't tell me you did this just to make the fight more challenging.
Akira raised his hands slightly.
"Relax. That's not the only effect."
Everyone froze for half a second.
"While demons grow stronger," Akira continued, "they also grow dumber. The more they drink, the worse it gets. But because they feel stronger, they can't stop drinking."
He smiled faintly.
"It's a perfect trap."
The sound of Muzan roaring echoed through the chamber as his tentacles continued to lash out, stronger than ever, but increasingly wild, uncoordinated, and brutal.
Erika frowned, eyes still fixed on the writhing mass of Muzan.
"But wouldn't he just grow stronger, too?" she asked. "That's dangerous, right?"
Akira nodded once.
"It would be, if that were all."
He looked directly at Muzan, voice steady.
"The poisons I injected into him are still inside his body. And with his intelligence reduced, he doesn't have the mental capacity to actively break them down anymore."
The realization settled heavily over the group.
"To be honest," Akira continued calmly, "if we left him like this, he'd probably die before daybreak on his own."
There was a pause.
"Still," he added, eyes narrowing, "it's better to kill him ourselves. We shouldn't leave something like this to chance."
Gyomei tightened his grip on his weapon and nodded deeply.
"That is true. We must finish this fight with our own hands."
Akira took a slow breath.
"Then let's finish this," he said. "Let's do this—Eclipse."
The moment the word left his mouth, the cool-looking jet-black armor covered his body.
Two glowing purple katanas materialized in his hands.
Akira stepped forward, armor humming with restrained power, eyes locked onto Muzan.
The final battle had begun.