After slaying the Twelve Kizuki, Upper Rank Four, Daki, the Blood Demon Art: Infinity Castle was immediately dispelled. The demons and swordsmen who had fallen into that alternate space almost instantly returned to the Yoshiwara entertainment district.
The sensation of spatial imbalance left both demons and swordsmen momentarily dazed.
At the very moment the Infinity Castle shattered and they reappeared in Yoshiwara, Muzan Kibutsuji—who had hidden himself away while desperately breaking down the medicine inside his body—fled into the distance without the slightest hesitation.
Fleeing had once been Muzan Kibutsuji's greatest strength.
It was also the ability he had once taken the most pride in.
Back then, Yoriichi Tsugikuni, the swordsman praised as a god or Buddha walking among men, had nearly severed his head in an instant and forced him to the brink of despair.
But so what?
Muzan had split his body into one thousand eight hundred fragments of flesh in that same instant. Even though Yoriichi had cut down over one thousand five hundred of those pieces on the spot, the remaining fragments had still escaped.
As long as even a single fragment survived, Muzan Kibutsuji would not die.
That had been the first time he was ever forced into a true corner.
Yet even then, what had it mattered?
No matter how overwhelmingly powerful Yoriichi Tsugikuni was, he still could not truly kill him.
Human life was fleeting. Even the strongest swordsman could live for only a century at most. Muzan had hidden in the shadows, waiting patiently for decades. When Yoriichi finally grew old and frail, his chance had come at last.
On that night of the red moon, Kokushibo, his subordinate, had found the aged Yoriichi Tsugikuni.
Even in his twilight years, Yoriichi still possessed strength at its peak. The speed and power of the single slash he unleashed were no different from his prime. Yet he never managed to complete that final strike. He remained standing in that same posture… and simply reached the end of his life.
No matter how powerful a swordsman, none could withstand the slow corrosion of time.
Therefore, even if the Demon Slayer Corps produced another swordsman on the level of Yoriichi Tsugikuni, Muzan would fear them—but he would never despair.
But now…
For the first time in his existence, Muzan Kibutsuji felt true despair.
At this moment, the splitting ability he had always relied upon was completely suppressed by Tamayo's drug. He could no longer divide himself into over one thousand eight hundred fragments of flesh in an instant as he had during his battle with Yoriichi.
Worse still, the one hunting him to the death this time was not a human whose life burned as briefly as a firefly.
It was… a demon.
He could feel it—this was a demon that was still growing stronger. If he failed here, he might spend the rest of his existence hiding in darkness, never again seeing the light of day.
He might not even be given the chance to hide.
For the first time, he tasted genuine, bone-deep despair.
…
He ran.
He kept running.
As the drug continued to spread deeper through his body, human traits began surfacing one after another. His breathing grew rapid and labored. Weakness flooded his limbs with increasing intensity.
Thud…
Long unaccustomed to the fragility of a human body, his legs suddenly lost all strength. The body that had been sprinting at full speed lost balance and crashed to the ground.
"It's over."
The thought rose in Muzan Kibutsuji's mind just as he lifted his head.
On the moonlit street ahead, Soma stood holding a blade. He had appeared at some unknown moment and was now watching him with calm, unwavering eyes.
Meeting that gaze, Muzan's crimson eyes flashed with fear. He staggered backward, his voice filled with bitter resentment.
"We are both demons… We are both demons! Why? Why are you standing with these Demon Slayers?!"
"Am I a demon?" Soma asked quietly, still watching him.
"Aren't you?!" Muzan roared.
"Have I ever devoured a human being?" Soma's voice remained calm.
"Who knows?! But once you become a demon, how could anyone possibly resist the desires that come with it? No demon can endure them!"
"That's right," Soma said softly. "No demon can endure the craving for human flesh and blood."
He looked straight at Muzan.
"Back then, without any warning or reason, you turned me into a demon. I had to constantly fight against that same unbearable hunger for human flesh…"
His voice dropped to a murmur.
"Even so… I endured it. All this time, I endured it."
He met Muzan's eyes.
"Even before I lost control completely, I kept suppressing the bloodlust. To this day, I have never once devoured even a single piece of human flesh."
Muzan's eyes widened in disbelief.
Among all the demons he had created with his own blood, not a single one had ever been able to resist the instinctive craving for human flesh. Even Akaza, whose obsession ran deeper than most, had ultimately been unable to endure it.
A gentle wind blew through the street.
Shinobu Kocho, who had arrived moments earlier, stood silently listening to the exchange between Soma and Muzan.
Her beautiful violet eyes remained fixed on Soma. Shock, complexity, and deep, aching concern flickered across her face. Shinobu, who hated demons with every fiber of her being, understood better than anyone just how overwhelming a demon's hunger for human flesh truly was.
Yet Soma had resisted it through sheer willpower alone.
In that moment, she remembered the promise she had once made with her sister.
The day she joined the Demon Slayer Corps, she had sworn to her sister that she would save the demons.
Yes… the idea of saving demons.
Back then, Gyomei Himejima had not understood it. In truth, even Shinobu herself had never truly held that belief. Toward demons, she had only ever felt hatred. She had only ever wanted to sever their heads and feel her blade pierce their flesh.
For years, that single desire—to behead every last evil demon—had never left her mind.
She had never once thought of saving them.
But now, for the first time… she found herself wanting to save a demon.
…
"I have never devoured a human," Soma continued, his voice cold. "And I can walk beneath the sunlight. So tell me—what makes you so certain that I am a demon?"
Muzan stared at him, eyes filled with a desperate, ancient longing—the very thing he had chased for over a thousand years.
"A demon is still a demon. It cannot be changed. You simply overcame the demon's weaknesses and became a perfect demon."
"Considering we are both demons," Muzan said, voice low and urgent as Soma stepped closer, "tell me. How did you overcome the weakness to sunlight? How did you become a perfect demon?"
He already knew his end was near. Yet in these final moments, he wanted—needed—to know the answer to the question that had tormented him for centuries.
Was it because of the Blue Spider Lily?
Soma did not answer.
He raised the Nichirin Sword.
"When you reach hell," he said quietly, "perhaps you will finally understand."
The blade fell.
A single strike infused with the radiant power of Sun Breathing carved through the night, aimed straight for Muzan Kibutsuji's neck.