One Piece: With Sign-in System

Inside the Infinity Castle.

Muzan had summoned all the remaining Upper Moons.

Upper Rank Two, the Demon Doma, responded to the call and arrived at the castle.

His rainbow-colored pupils scanned the strange architecture around him as a flicker of surprise surfaced on his face.

An Upper Moon meeting?

It had been many many years since the last such gathering.

To be summoned like this could only mean… one of the Upper Moons had fallen.

But who?

The first figure he saw was a demon clutching a biwa—the castle's sentinel, and Muzan's personal attendant who resided within the Infinity Castle—Nakime.

A deep, resonant strum of the biwa echoed through the air.

With that sound, the Fifth Upper Rank appeared: the vase demon, Gyokko.

Then came the Fourth: the clone demon, Hantengu!

Next, Upper Rank Six, the sibling duo: Gyutaro and Daki.

Finally, the First Upper Rank, the blade-wielding demon, Kokushibo.

As each of the Upper Moons arrived one by one…

Muzan emerged—this time taking the form of a pale young boy.

Doma's gaze flicked around as he quickly realized—someone was missing.

Upper Rank Three—the martial demon, Akaza… wasn't here.

"Greetings, Lord Muzan."

All the Upper Moons knelt before Muzan, who stood silently in front of them. His crimson, vertical pupils were ice-cold and devoid of emotion as he looked down at the demons bowing before him.

"Akaza is dead. The Twelve Kizuki now stand incomplete."

A visible shiver passed through Hantengu, Gyokko, Gyutaro, and Daki.

Doma, who had just confirmed the truth, was visibly surprised.

"That Akaza… actually died? Now that's rather unexpected," he murmured with a hint of a chuckle.

Behind the screen, Kokushibo remained expressionless.

In his view, Akaza was simply not strong enough. His death? Just the natural order of things.

"For over a century, the Upper Moon ranks have remained unchanged… but now, for the first time, there's a vacancy."

"The mighty Upper Rank Three… killed by mere Demon Slayers."

Muzan's frigid voice rang through the Infinity Castle like the hiss of steel drawn across stone.

"I created all of you for two purposes—find the Blue Spider Lily, and eliminate the Demon Slayer Corps. And yet, after all these years, not only is there no trace of the Blue Spider Lily, but the Ubuyashiki clan still lives—and now even Upper Rank Three has been killed by the Demon Slayers."

"Akaza… you have truly fallen."

Veins throbbed across Muzan's forehead, his rage starting to bubble visibly beneath his skin.

The demons present—Hantengu, Gyokko, Gyutaro, and Daki—were all gripped with dread. Their hearts pounded wildly with fear.

Gyokko began sweating profusely. "L-Lord Muzan! I'll go right away! I'll hunt down the Demon Slayers and kill every last one of them!"

Muzan's icy gaze locked onto him.

"And what good would that do?"

"Did you not understand what I said?" Muzan's voice dropped into a deadly calm. "I want the entire Demon Slayer Corps annihilated. Not just hunted down. Obliterated. I want them crushed to death with such finality that they never again darken my path!"

"This is not some complicated task. And yet all of you have failed to accomplish it. Why? Why are you even here? What is the purpose of your existence?"

The pressure of Muzan's fury swept over the room like a suffocating tide.

Every demon present began trembling uncontrollably. Their demonic blood boiled inside their veins, their knees giving out beneath them as they collapsed in terror.

Their fear of Muzan wasn't just psychological—it was written into their very DNA.

Hantengu collapsed, weeping. "Please… forgive us! Have mercy, my lord!"

Gyokko pressed his head hard against the floor. "Y-Your servant will immediately locate the Demon Slayer headquarters!"

Doma, ever theatrical, let out a sigh. "Ah… I'm not really good at tracking or searching. What ever shall I do?"

Kokushibo, who hadn't spoken in what felt like centuries, finally uttered a fragmented reply in his deep, emotionless tone:

"Ubuyashiki… has hidden… their whereabouts… too well…"

"I'm growing tired of this," Muzan said at last, his blood-red, slit-pupiled eyes sweeping across the group like the edge of a blade. "If you can't find the Ubuyashiki clan… if you can't destroy the Demon Slayer Corps to prove your worth…"

"You already know what comes next."

"Do not—ever—make me angry again."

A shudder ran through the hearts of the remaining Upper Moons.

"From this moment on, Nakime shall be Upper Rank Three."

The biwa-playing demon lifted her head slowly. Beneath the veil of her bangs, a giant eye opened on her forehead—with the character "Three" etched into its center.

...

Demon Slayer Corps Headquarters—Ubuyashiki Estate

"What? An Upper Moon has been defeated?!"

"And it was Upper Rank Three?!"

Ubuyashiki Kagaya and the Hashira seated around him were visibly shaken by Tanjiro's report.

Tanjiro, sitting properly before them, nodded seriously. "Yes. Inosuke and I both saw it with our own eyes. The demon had the words 'Upper Rank Three' carved into both of its eyes. Its strength was immense—without a doubt, it was one of the Twelve Kizuki."

The Hashira exchanged glances, stunned.

Tengen Uzui leaned forward, his expression serious. "Kid, tell us everything that happened. Leave nothing out."

And so Tanjiro began recounting the events aboard the Mugen Train in meticulous detail.

When he described the demon's appearance, Kagaya's gentle voice affirmed his conclusion. "Yes… the demon you encountered was Akaza—Upper Rank Three, the Battle Demon. Over the past few decades, many Hashira have fallen at its hands."

Kyojuro Rengoku crossed his arms with a deep frown. "To think such a formidable opponent appeared... If I'd known, I would've gone too."

Uzui stroked his chin thoughtfully. "The battle between Akaza and Mr. Ron… it must have been intense. But for him to defeat Akaza alone… as expected of Ron."

Mitsuri Kanroji turned anxiously to Tanjiro. "Was Mr. Ron injured at all?!"

Tanjiro quickly shook his head. "Nope. The fight ended very quickly."

Everyone stared at him, dumbfounded.

And then, when they heard that Ron had shattered Akaza's body with a single punch, and crushed his head with one stomp…

The entire room fell dead silent.

"O-One punch…" Rengoku's eyes widened slightly. "You're saying he… he killed Upper Rank Three with just one punch?!"

Tanjiro nodded again.

Uzui was frozen in disbelief.

Sanemi stood there like a wooden statue.

Muichiro remained expressionless as ever.

Mitsuri was absolutely stunned, her face full of shock.

They had known Ron was strong—terrifyingly strong—but to take down an Upper Moon with one punch… was that even within human limits?

Even Shinobu Kocho, who knew Ron better than the others, was left momentarily dazed by the report.

To kill Upper Rank Three in one blow… then what about Upper Rank Two?

The silence lingered for a long while.

It was Ubuyashiki Kagaya's voice that finally broke it.

"A hundred years…"

His normally calm face showed rare emotion. His eyes gleamed, his voice slightly trembling with passion.

"For a century, the Upper Ranks have remained unshaken… until now. My friends, do you understand? This is the sign we've been waiting for. The omen of change—ushered in by Mr. Ron."

"The ripples caused by Mr. Ron's actions will only grow larger… and eventually, they will reach that man—Kibutsuji Muzan himself! Our task now is to seize this opportunity… and ensure he never escapes again!"

...

In a Small Courtyard Near the Butterfly Mansion,

Ron lay reclined in a chair, eyes closed.

His Observation Haki—laced with the precision of a sharpened mind—spread out from his body in every direction, covering a radius of over a hundred kilometers.

Within that web, not even a shadow of a demon could hide. Every movement in the darkness, every space-time distortion around the Infinity Castle… he saw it all.

He had already locked onto the location of the Infinity Castle.

If he wished, he could step into it right now.

Creak.

The courtyard gate opened with a soft groan.

Shinobu Kocho stepped in quietly and approached him, hesitating slightly.

Without opening his eyes, Ron spoke calmly, "If you've got something to say, then say it."

Shinobu hesitated for a moment longer, then asked softly, "Didn't you say you wouldn't get involved in the conflict between the Demon Slayer Corps and the demons? Then why…"

"I couldn't just stand by and watch a disciple I carefully taught get killed, could I?" Ron replied flatly. "Besides…"

"Besides?"

He opened his eyes, gazing through the pink cherry blossom branches at the open blue sky above. A serene smile tugged at his lips.

"I've decided… it's about time I leave."

Shinobu's violet eyes widened slightly.

"…Eh?"

Ron turned to her and smiled. "So I won't waste any more time waiting for Kibutsuji Muzan to come knocking."

"I'll take you all… to find him instead."