"Lord Muzan, I might have someone useful."
Upper Moon One, Kokushibo, spoke calmly.
Muzan glanced at his "colleague." Unlike his ruthless dismissal of Gyokko earlier, this time he didn't lash out. While Kokushibo was still far inferior to him, there was no one else more powerful among the demons. Muzan was willing to grant him an opportunity to speak.
"Go on."
"A while ago, during a patrol, I encountered an interesting individual."
"Keep talking."
"His name is Kaigaku. If you're interested, my lord, you can simply have Nakime bring him here to the Infinity Castle."
With a flick of Muzan's hand, Nakime immediately understood his command.
A silhouette was summoned to the Infinity Castle.
Pointed ears, long fangs, pale skin, black tiger-striped markings across his face—he was unmistakably a demon. But the Nichirin Blade on his back and the uniform he wore were clearly that of the Demon Slayer Corps.
"A demon… who used to be a Demon Slayer?"
Muzan narrowed his eyes.
Kaigaku, still recovering from the shock of his sudden teleportation, instantly broke into a cold sweat.
He could feel death breathing down his neck.
"You get one chance to explain yourself."
"My lord! I'm Kaigaku, former Thunder Hashira Jigoro Kuwajima's senior disciple! I can provide valuable information on the Demon Slayer Corps!"
Kaigaku blurted it all out. He hadn't fully chosen to become a demon, but now that he had—living was all that mattered. Human or demon, it didn't make a difference anymore.
"Information on the Demon Slayers? And what am I supposed to do with that!?"
Muzan suddenly exploded in rage.
So this was what Kokushibo had in mind? Some trivial intel on the Demon Slayers? As if that could satisfy his fury?
Muzan had never truly feared or respected the Demon Slayer Corps. He simply found them unworthy of serious attention.
But then… something clicked.
Someone from the Corps…
"You might be of use after all."
The suffocating air of death lifted. Muzan's killing intent evaporated as quickly as it had appeared.
This is the King of Demons… so terrifying, Kaigaku thought, his heart still racing.
Suddenly, Muzan appeared right in front of him.
"Next time, don't even think unnecessary thoughts."
BAM!
He stomped Kaigaku's head into the ground.
"Now, I have a task for you. You should still know where your old master is, right?"
"Kill him. And make sure everyone knows you did it."
"Kill… my teacher!?" Kaigaku's pupils dilated in shock.
"What's wrong? You don't want to?" Muzan twisted his foot harder against Kaigaku's head.
"N-No, my lord. I'll do it."
Truthfully, Kaigaku had always harbored resentment toward his former master. He could never understand why Jigoro chose to have him, the senior disciple, share succession with that pathetic Zenitsu—someone who only ever used one form. A complete disgrace.
If he could watch that old man die in agony, he'd feel nothing but pleasure.
"It's just… making sure everyone knows, and actually defeating him—he used to be a Hashira, and I'm… I don't have that kind of strength."
"Don't worry. You will."
Without hesitation, Muzan poured his blood into Kaigaku's body.
"AAARGHH!!"
Kaigaku let out a guttural scream as power surged through him. His aura instantly skyrocketed several levels.
"Now go. I don't care what you have to do. Just make sure my will is fulfilled."
Muzan lost interest in Kaigaku then and there. That was all he was good for. If he failed, Muzan would simply detonate the blood inside him and erase him like the insignificant insect he was.
Nakime transported Kaigaku out of the Infinity Castle.
Once he was gone—
"All of you—aside from Daki—are to follow Kaigaku."
Muzan's gaze swept over the remaining Upper Moons, voice icy with command.
"If the Demon Slayer Corps sends anyone, or if that boy Yohan appears… I don't care who it is. Kill them all."
"Yes, my lord," the Upper Moons bowed their heads, voice unified.
…
"Lord Muzan, Daki requests an audience."
Dressed in her ornate oiran robes, Daki entered and knelt gracefully at Muzan's side.
"Why won't you let me join the mission, my lord?" she asked softly.
"Are you questioning me?"
"N-No, of course not, Lord Muzan! I was wrong!"
Her face turned ghostly pale, trembling in terror.
"You don't need to understand, Daki. Your role is to stay in the pleasure district and continue gathering information."
"Specifically… on the Blue Spider Lily."
"That is the only thing that truly matters to me."
"Yes, my lord. I shall take my leave now."
Daki promptly vanished from the Infinity Castle.
Muzan had long since lost faith in the Upper Moons. But their true value had always been in tracking down the Blue Spider Lily. Kaigaku's mission was nothing more than a small act of revenge on the Demon Slayer Corps.
If some of the Upper Moons died in the process… it didn't matter.
So long as he lived, that was all that mattered.
…
At the Butterfly Mansion—
This was the second time Kagaya Ubuyashiki, the master of the Demon Slayer Corps, had come in person.
Compared to before, his condition had worsened. The curse on his body was accelerating, ravaging him from the inside out.
Had Yohan not delivered such shocking news, Kagaya would never have left the estate.
"Master, you didn't have to come personally," Yohan said, gently supporting the frail figure.
"You could've just summoned me."
He looked at the man with worry. Kagaya's body seemed so fragile now that Yohan feared a single touch might break him.
"No, Yohan-kun… I had to come."
"After you slew Upper Moon Two, Doma… and now Upper Moon Three, Akaza…"
"This may not seem like much to you, but I must thank you—not just as the master of the Demon Slayer Corps, but as a man."
"I know I don't have much time left."
"But because of you… I finally believe we can kill Muzan Kibutsuji."
"Please, lend us your strength until the very end."
With that, Kagaya bowed deeply—kneeling, pressing his forehead to the floor. The deepest, most solemn gesture of respect.
Yohan watched silently, letting the moment pass without interruption.
His voice, when he finally spoke, was steady and firm:
"Master… rest assured. This will all end soon."
He understood the man's resolve.
And he would never let him down.
But in truth, Yohan wasn't doing any of this for thanks or glory.
He was doing it—because he wanted to.