"Caw—!! Caw—!!"
"Muichiro Tokito! Upper Rank Five! Defeated!!"
The crows that had been transported into the Infinity Castle together flew swiftly through its labyrinthine corridors, guiding the Demon Slayer Corps members while loudly broadcasting exhilarating news to everyone.
Kokushibo paid no attention at all, as if none of it concerned him.
He lowered his head and stared at the wound on his chest, a gash that still refused to heal, writhing with flames.
Complex emotions intertwined within his six eyes: jealousy, anger, incomprehension, and a warrior's fervor that had finally erupted at this moment.
"For hundreds of years... among humans, aside from that man, you are the first to force me to this point."
His voice was no longer calm. Each word carried a resonance that seemed to make the surrounding space tremble.
As his words fell, the demonic aura around him began to swell and surge at a terrifying speed.
"Since your swordsmanship has touched the realm of the divine... then I, too, shall respond with everything I possess as a demon."
Crack—crack—!!
The sound of bones breaking echoed from Kokushibo's direction.
His body grew noticeably more robust in an instant. From his back, carapace-like bone spurs bulged outward, and the veins on his previously cold and resolute face writhed like black serpents.
As Kokushibo released his demonic power in full, the long sword covered in eyeballs emitted a shrill and ghastly screech.
The blade itself began to grow wildly.
Bone-like material expanded outward from the hilt.
In the blink of an eye, the blade had nearly doubled in length. Several branching blades sprouted diagonally along both sides of the main edge, each one also covered in rotating eyeballs.
It no longer resembled a sword.
Instead, it looked like the spine torn from a demon of hell.
"This is..." Asuka paused, staring at it in surprise. "Is your sword also a Zanpakutō?"
"Zanpakutō?"
The word was utterly unfamiliar to Kokushibo. He could not comprehend a term that originated from another world entirely.
"Nonsense."
Kokushibo suddenly stepped forward.
The bricks and rubble beneath his feet, already reduced to ruins, shattered instantly.
[Moon Breathing: Fourteenth Form - Catastrophe, Tenman Crescent Moon]
The grotesque blade swept through the air, instantly releasing several enormous serrated moon-shaped slashes that crisscrossed and covered nearly every blind spot around Asuka.
Just like before, each moon slash contained countless tiny fragments shaped like blades, only now they were faster, more numerous, and far more ferocious.
This was the power of his demon blade, capable of amplifying Kokushibo's already deadly Moon Breathing even further.
Swish—!!
The ground where Asuka had been standing was flattened by several meters.
Although he avoided the attack by using Thunder Breathing combined with the explosive force of concentrated spiritual pressure, a stray fragment of the moon slash still grazed his right arm.
Blood instantly stained his clothing.
"Such heavy sword energy..."
Asuka could feel that the opponent's blade had not only grown longer, but the amount of demonic power it carried had multiplied several times over.
"It seems your sword is thirsting for my soul."
Asuka slowly landed amid the overwhelming tide of sword energy, no longer concealing his aura.
The mark burned as it crawled up his cheek. His spiritual pressure perception expanded to its absolute limit, allowing him to see even Kokushibo's bones and internal organs.
Buzz—!
A crisp hum rang out as the Zanpakutō in his hand began to glow with a blazing crimson light.
"So it really is a crimson blade..." Kokushibo's gaze turned solemn. He could feel Asuka's presence rising to yet another level.
At the same moment, both of them exploded into motion.
One red, one black—two afterimages clashed violently across the ruins.
Clang! Clang! Clang! Clang!
Having unleashed his demon form, Kokushibo's swordsmanship had already surpassed the realm of human comprehension.
The branching blades on that monstrous sword could not only block attacks but also function like independent short swords.
When Asuka twisted his body to rush forward, those branching blades could bend in unnatural ways and stab directly toward his back.
Yet Asuka, who had fully mastered five Breathing Styles, was no longer a human who could easily be matched.
His spiritual pressure spread outward, forming a domain centered on himself. Any fluctuation in the air currents could not escape his perception.
Though Kokushibo's sword techniques were extremely fast and ferocious, they still could not truly threaten Asuka's life.
The two of them darted and flashed through the collapsing Infinity Castle, their bizarre blades colliding again and again.
From the dojo they fought to the outer platforms, then dropped once more into the collapsing ruins.
Crimson and silver sword light shredded the surrounding tatami rooms and corridors.
Every shockwave created by their clashes was powerful enough to annihilate any demon foolish enough to approach.
Just as Asuka and Kokushibo were locked in fierce battle, thunder in another corner of the Infinity Castle had already reached the limit that human eardrums could endure.
The terrain here was extremely treacherous—a fragmented space composed of countless broken corridors floating above a bottomless abyss.
"Hahahaha! Zenitsu! That pathetic stray-dog look of yours hasn't changed at all!"
Kaigaku leapt high into the air, the black lightning patterns on his back looking especially vicious in the darkness of the Infinity Castle.
His Nichirin Blade crackled with pitch-black lightning.
It was a mutated form of Thunder Breathing created after he consumed demon blood.
"See it? This is true power! A strength that useless old man could never experience in his entire life!!"
"Breath of Thunder: Second Form – Rice Spirit!!"
Five slashes wrapped in black lightning shot out instantly, blasting the corridor beneath Zenitsu's feet into fragments.
Not only that, the Thunder Breathing sword forms in his hand constantly shifted and transformed, bombarding Zenitsu relentlessly.
Explosions erupted everywhere.
Zenitsu rolled across the ground in embarrassment.
His haori was already tattered, and his body was covered in bloody wounds.
Those black lightning bolts carried powerful corrosive properties, steadily eroding his life force.
But he said nothing.
Beneath that short golden hair, his eyes were cold and emotionless.
The grief he had suppressed to the extreme made the very air around him heavy.
"Grandpa..."
Zenitsu finally spoke.
His voice was hoarse and trembling.
"Grandpa... committed seppuku for your sake..."
"There wasn't even anyone to be his second... he died in agony!"
Kaigaku's body paused briefly in midair.
Then an even more frenzied mockery spread across his face.
"Serves him right!"
"That stubborn old fool insisted on passing the inheritance to trash like you! If he had just given me all the essence earlier, would I have turned into a demon?"
"Shut up..."
"What's wrong? Am I not right? Then prove it to me! Show me the value of the First Form that that useless old man treasured so much!"
Zenitsu slowly lowered his center of gravity.
The rage within him finally reached a breaking point.
He gripped the sword hilt tightly.
The scattered electric arcs around his body began to shrink wildly into the scabbard.
Then—
They exploded outward!
Reach the absolute peak.
"W-What is this?!"
Even Kaigaku, who had already become a demon of the Twelve Kizuki, shuddered at the sight.
He could feel a massive terror descending upon him.
In panic, he swung his demon blade wildly, pouring all his demonic power into it.
"Breath of Thunder: Fourth Form – Distant Thunder!!"
Black spherical lightning shot toward Zenitsu like falling meteors.
However—
That golden flash arrived even earlier than the lightning.
In an instant, the darkness of the Infinity Castle was completely torn apart.
What burst forth from the Nichirin Blade was not ordinary electricity.
It transformed into a giant dragon made of golden lightning, roaring as it tore through the void.
The speed was so overwhelming that even gravity could not react.
Space—and even time—seemed to lose all meaning.
Kaigaku's pupils shrank violently.
He did not even feel pain.
All he saw was a golden blade of light, brighter than the sun, slicing across his neck.
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