In the basement of the Akatsuki Trading Company headquarters, a large ritual hall heavily protected by a barrier.
Today, Akira's strongest forces gathered in this place, usually used as a research facility.
The air was heavy, and the space itself seemed to tremble from the aura each of them emitted.
"Preparations are complete."
Akira stood at the center, dressed in a suit as black as pitch.
A long shadow stretched behind him, and within that shadow, aberrant beings flashed their eyes.
Kiyohime, the yandere serpent wreathed in blue flames; Tamamo-no-Mae, the nine-tailed fox one step away from godhood; Tamamo Cat, baring her wild claws; Benienma, the princess with the King Enma's sword at her waist; Shuten Douji, the leader of oni, holding a sake bottle with a bewitching smile; Ushigozen, clad in black armor imbued with lightning; and Hokusai (Oei), swirling her brush with a seductive grin.
All Servants were assembled, except for Nobunaga who was dispatched, and Okita and Ushiwakamaru who were with the Demon Slayer Corps.
Along with them were Mitsuri, Shinobu, Kanae, and Tsubaki.
"Our target isn't a simple hunt. We're swallowing Muzan's stronghold, the Infinity Castle, whole."
Akira's voice resonated solemnly.
"We have two objectives: capture Nakime, the administrator of the Infinity Castle, and seize control. And recruit Upper Moon One, Kokushibo, who uses Moon Breathing. The rest… kill or drive out if they get in our way."
At Akira's gesture, an old man bound in the corner was dragged out, trembling.
Upper Moon Three, Hantengu. His ego had already been shattered by Tamamo's curse, reduced to nothing but a coordinate transmitter.
"Eeek…! S-scary! Spare me…!"
"Don't cry. You're an excellent compass."
At that moment, Hantengu's body began to blur. Muzan, detecting Akaza's demise, had issued an emergency summoning order for the Upper Moons in a rage. Space twisted, attempting to summon Hantengu back to the Infinity Castle.
"Now! Oei!"
"Understood, my lord! With this brush, I shall paint the other side of the world!"
Hokusai (Oei), wielding a giant brush, scattered ink into the void.
It wasn't mere painting. It was a mystical art that fixed dimensional coordinates and forcibly opened a path.
With a gurgling swirl, the ink formed a massive black gate.
They had forced it open, wedging through the gap as Hantengu was sucked in.
"Let's go! We finish this before Muzan arrives!"
Akira took the lead, leaping into the dimensional gate. His army poured in after him like a tidal wave.
A ding~
The Infinity Castle—a bizarre labyrinth of wooden buildings with gravity twisted and directions reversed.
At its center, a heavy silence hung over the central platform where the Upper Moons gathered.
Due to the previous hunts, the former Upper Moons—Doma, Gyokko, and Gyutaro—were all dead. Daki had also joined Akira's side, so the Upper Moons had declined in quality compared to before.
And now, Akaza, who had been promoted to Upper Moon Two, was dead too.
All that remained were Upper Moon One, Kokushibo, and Nakime, newly made Upper Moon Four.
And to fill the vacancies, Muzan had hastily promoted new Upper Moons of unverified strength, who stood cowering.
"This time, Akaza… after Gyutaro, Gyokko, Doma… all defeated. The Demon Slayer Corps' doing? The Hashira's level… seems to have grown stronger on average than in my era."
Kokushibo muttered, his six eyes flashing. The new Upper Moons couldn't even breathe properly under the pressure he emitted.
Right at that moment.
KABOOM!!!
With a deafening roar as if the ceiling were tearing apart, a black wave cascaded down from the void like a waterfall.
"Wh-what is that?!"
"Intruders?! How did they get here?!"
The new Upper Moons screamed.
But before they could grasp the situation, Akira's legion had already landed.
"Target confirmed! It's Nakime! Benienma!"
The moment Akira's order fell, Benienma kicked off the ground and soared.
Her movement far surpassed the demons' kinetic vision.
"Suzumegaeshi!"
Slash! Slash! Slash!
Invisible slashes split the space. Nakime's arms, about to strum her biwa, flew off at the shoulders, and her legs were severed at the thighs.
"...?!"
Nakime had no time to scream. With the loss of her hands, the medium for her Blood Demon Art, control of the Infinity Castle temporarily paralyzed, and the building's movement stopped.
"Too late."
Seizing the opportunity, Akira closed the distance in an instant, appearing before Nakime.
He gruesomely gripped the head of Nakime, who lay sprawled with limbs severed, with one hand.
Squelch!
Akira's fingers dug into Nakime's skull. Crimson tentacles directly infiltrated her brain and neural network.
Muzan's cells tried to resist, but Akira's cells, those of a perfected being and an apex predator, crushed and devoured them.
"Kuh… ghh… aaah…"
Nakime's body convulsed violently. Her single, giant pupil trembled. The Upper Moon character vanished as Nakime collapsed.
The hack was complete.
With that, the administrator privileges of the Infinity Castle had been usurped.
"You… who are you?!"
The first to react was, of course, Upper Moon One, Kokushibo.
He instantly assessed the situation and drew his sword to eliminate Akira. A grotesque sword with eerie eyeballs embedded throughout its blade.
"How dare you… this place…"
Moon Breathing, Eighth Form: Dragon Tail Circle.
As Kokushibo swung his sword, countless crescent-shaped slashes charged toward Akira's neck, tracing irregular trajectories.
A storm of slashes filled the space.
But Akira didn't even look back.
CLANG!!!
With a tremendous impact, Kokushibo's slashes were blocked mid-air.
A woman clad in black armor, wreathed in blue lightning.
Ushigozen had intercepted Kokushibo's strike head-on with her own sword.
Zap! Crackle!
"To aim your blade at my Master. How insolent, fallen samurai."
Ushigozen's cold rebuke. The lightning emanating from her sword nullified the moon slashes and forced Kokushibo back.
"Hoh… to block my sword…"
Kokushibo's six eyes narrowed. For the first time in centuries, a pressure equal to or greater than his own.
Unlike other demons, Kokushibo was clearly at Servant-level strength. A worthy opponent that sparked Ushigozen's competitive spirit.
"Enough. Ushigozen. Don't kill him."
Akira, having fully dominated Nakime, slowly turned around. In his hand, Nakime hung like a bloody doll.
"Let's clean up first. Too much clutter."
Akira manipulated Nakime's nerves.
A ding~
A strange biwa sound echoed through the Infinity Castle. Then, except for Kokushibo and the guide Hantengu, the feet of the new Upper Moons hastily installed by Muzan suddenly gave way.
"Wh-what is this?! Why is the Infinity Castle doing this?!"
"We're falling!"
They were forcibly teleported out of the Infinity Castle, ejected somewhere thousands of meters in the air, screaming.
With the clutter gone, only silence remained in the vast Infinity Castle.
Akira slowly walked toward Kokushibo. Behind him, Kiyohime, Shuten Douji, and the other Servants lined up, emanating overwhelming killing intent.
Kokushibo didn't sheathe his sword, but he couldn't recklessly attack either.
His instincts warned him. That man was dangerous. A ruler of the abyss itself, different in nature from Muzan.
"Pleased to meet you. Tsugikuni Michikatsu. Or should I call you Kokushibo now?"
"...!!"
Kokushibo's pupils shook. The name from his human days. No one had spoken it for centuries, and this unknown man knew it.
"How… do you know my name? Who… are you?"
"I am Akira. The king who will reign over this night anew."
Akira approached until he was right in front of Kokushibo, his hand in his pocket.
Ushigozen guarded him warily, but Akira remained perfectly composed.
"Kokushibo. You pursue strength. To surpass your brother Yoriichi, you abandoned even your pride as a samurai and became a demon. You gave up everything—family, your life as a human."
"… Shut up."
"But… was that possible under Muzan? Centuries have passed, yet you haven't even stepped on Yoriichi's shadow. Muzan can't give you true strength. He's just a coward hiding from the sun."
At Akira's provocation, Kokushibo's killing intent exploded.
But Akira didn't bat an eye, pulling a small glass vial from his chest.
Inside, a mysterious blue-glowing liquid sloshed.
"The Blue Spider Lily."
Kokushibo's six eyes widened simultaneously. That which Muzan had searched for over a millennium.
The legendary flower that makes demons into perfected beings.
"This is the essence of the medicine that overcomes the sun. Of course, I can't give this to you, but I've ingested it. I became a perfected being that even Muzan dare not covet. And my blood can evolve you one step further."
Akira shook the vial.
"A swordsman freed from Muzan's curse, walking proudly under the sun. The realm Yoriichi reached, or beyond. I can make that happen."
"...."
"Come with me, Michikatsu. Not as Muzan's pawn, but with me, to explore the true pinnacle of nothingness. The path of the sword you desire, eternal time, a perfect body. I'll give you all of it."
Akira extended his hand. It was an irresistible devil's offer.
Loyalty to Muzan never existed. Only the obsession to grow stronger, the inferiority driving him to defeat his brother.
And the man before him promised what Muzan couldn't: overcoming the sun and evolution.
Kokushibo's blade slowly lowered.
Within the twisted space of the Infinity Castle, the second strongest swordsman in history prepared to accept a new master.