The moon hung high over the dense forest, its silver light weaving through the thick canopy like threads of a celestial loom. Towering pines whispered in the wind as if they feared what lay beneath them, as if nature itself bowed to the presence that dwelled in this forgotten valley—deep within the mountains where the sky was always painted with mist and blood. There, nestled between cliffs draped in ancient fog, stood a lone Pagoda, vast and magnificent.
Unlike any structure in the lands of men, this one breathed with a stillness unnatural. Black lacquered wood lined with gold veins rose like bones into the night. Wind chimes made of hollow demon bones rang gently, echoing a melody no human would dare to hear twice. The stone path leading to the entrance had been carved from the most emmaculate of materials. Here resided no ordinary demon—this was the sanctum of Kokushibo, the Legendary Upper Moon One. A creature of divine wrath and ancestral torment.
He sat still upon a raised tatami platform in the grand chamber at the heart of the pagoda, his many swords resting silently behind him like the tails of a coiled dragon. His eyes—six of them—glowed with eerie grace, their focus fixed on the burning incense that drifted in front of him.
Kokushibo's form was as composed as a sculpture, and yet, beneath that stillness brewed a hunger far deeper than flesh—a hunger to get stronger, to perfect, to remember. His long raven hair flowed down his back like silken shadows. His robes, once ceremonial, now carried symbols of ancient power written in a lost language. On the walls of his chamber hung scrolls—records of martial techniques and information about foes he had faced, and those who had dared to dream of slaying him.
This world was no longer the fragile one it once was.
The Demon Slayer Corps had grown, evolved. Where once there were nine Hashira, now stood fifteen—each a master of forms so refined they rivaled the gods of old. Breathing Styles had diverged and recombined into new lineages. Each passed down through generations and carved in blood. Their swords shone brighter, their wills burned stronger. Even the lowest ranks of the Corps had grown exponentially stronger.
Yet the demons, too, had changed.
The Twelve Kizuki had doubled in number—now the Twenty-Four Kizuki, divided into Upper and Lower Moons with twelve in each rank. Each more horrifying than the last, born from Muzan Kibutsuji's ever-expanding madness and hunger for supremacy alongside his growing power. They were no longer just monsters—they were warlords of death, horrors in flesh. The world had become a living battlefield where the strong were devoured. Even the population was growing. More chances for demons to devour, more chances for Demon Slayers to recruit.
And in this grand cycle of evolving chaos, Kokushibo remained unchanged, a silent observer, an undying tyrant cloaked in solitude. Once Michikatsu Tsugikuni—a man, a brother, a warrior—now nothing more than a memory devoured by his pursuit of strength. His loyalty to Muzan was undeniable and that alone made him the most trusted associate to the Demon King.
The room was silent save for the crackle of the incense and the low drone of the wind brushing against the shoji walls. Kokushibo's breathing was near nonexistent, his form statuesque in its stillness. Deep within the folds of meditation, he drifted in that void between the present and the forgotten—a place where memory dissolved and instinct ruled.
And then—it came.
A ripple through the air. A pulse like a claw scraping against his very soul. It was not pain. It was not fear. It was command.
The Demon King had summoned him.
After forty years of silence—forty years where not once had Muzan Kibutsuji intervened in Kokushibo's work—his voice echoed directly within the mind of his most flawless creation. Smooth. Cold. Absolute. The last time the Demon King had summond him was the day, Kokushibo single handedly wiped out 6 of the Hashiras.
In the same breath, the air around Kokushibo shifted. The incense flames bent sideways as if bowing to a presence greater than themselves. From the shadows behind him, a melody arose—deep and mournful. The haunting notes of a biwa. The sound was unmistakable.
Nakime.
The walls of the pagoda began to tremble, stretch, and dissolve into an endless expanse of darkness. Tatami turned to stone. Shadows bled across the floor like living ink. The room fragmented, folding in on itself as if the fabric of reality had been plucked and plucked again. And then, in the blink of an eye, Kokushibo was no longer in his forest sanctum.
He stood in the sprawling halls of the Infinity Castle, a dimension twisted into endless layers of shifting architecture, floating rooms, and impossible gravity. The sky was a ceiling. The ground was a void. Blood-stained sliding doors opened and closed like breaths. And at the center of it all was Muzan Kibutsuji sat on a simple thorne like chair.
His form was regal, as elegant as it was terrifying. Long black robes draped like shadows incarnate. His skin pale, near-luminescent, eyes crimson with divine malice. He did not rise. He did not need to. The very air trembled in reverence of his presence.
Kokushibo knelt silently, not out of fear, but understanding and loyalty. This was no ordinary call.
"My lord," he said, his voice like a blade sliding from its sheath. "It has been long."
Muzan stared down at Kokushibo, his expression unreadable. "Rise," he said, his voice soft but carrying the weight of gods.
Kokushibo obeyed.
"I have not called upon you in four decades," Muzan began. "You have performed your duties with perfection. Your blade and skill has made my pursuit of strength easier. There has never been a need… until now."
He gestured with a single elegant finger. The space behind him shifted, showing a moving vision—a blood-red scrying portal. Within it, chaos reigned. Forests alight with flame. Hills strewn with severed trees and corpses. Demons on the run. And warriors—countless Kinoe-ranked Demon Slayers, flanked by two active Hashira and eight of the recently retired fifteen. Veterans who still moved with lethal grace.
In their midst were ten female demons, all grievously wounded, all struggling to fight through waves of steel and flame.
"The demons under attack are Upper Moon Five, Six, Eight, and Lower Moon One and Two alongside three weaker demons," Muzan said. "All female. And they are outnumbered."
Kokushibo's gaze did not waver, but his tone betrayed curiosity. "Their survival chances are minimal. Upper Moon Five alone can battle multiple Hashira—but that only stands with 2 hashiras not against ten Hashira and a hundred elite slayers… even she will fall."
None dared talk openly with the Demon King, none dared talk unless explicitly told to. Kokushibo however was Muzan's aide, brains and the only demon who apart from the Demon queen had Muzan's permission to talk to him freely.
"Indeed," Muzan said darkly. "That is why I summoned you."
Kokushibo tilted his head, eyes flashing. "You have never risked such a gathering of strength. Why now? Why do you send me, instead of letting them die and replacing them as you've done before?"
Muzan's voice dropped to a low, chilling growl.
"Because two among them are my daughters."
The silence that followed was deafening.
Kokushibo's many eyes narrowed slightly. "Your daughters?"
Muzan stood now, his aura rippling outward with cold finality.
"Born from my blood and the womb of my consort—a demoness I chose carefully. Two daughters, twins. Carriers of my essence. Potential of unseen amounts."
"I did not expect to feel anything," Muzan interrupted. His voice was lower now. "But when I saw them... when I held them in my arms—I understood something I never had before. Not as a man. Not even as a demon. I felt... divine. As though they were crafted not of blood and bone, but of my very essence."
"A sense of something fatherly bloomed within me."
Muzan's eyes flared red. "I cannot move from here. I am on the verge of perfecting a medicine—one that must be monitored constantly. My attention cannot break from it for even a moment."
Kokushibo rose, his hand already resting on the hilt of his blade.
"Understood, my lord. It shall be done soon."
The discordant strum of Nakime's biwa reverberated like a gong across realms. Reality folded.
And Kokushibo was gone.
He reappeared without sound atop the thick branch of a towering cedar, its trunk shrouded in moonlit fog. The forest was vast, its undergrowth torn and blood-streaked. The scent of violence clung to the air like rot on flesh. He stood upon a ridge looking at the forest infront, eyes glowing softly beneath the shadows of his long hair. Though the trees swayed gently in the night breeze, there was no wind. Only killing intent, pulsing through the forest like a silent scream.
Kokushibo remained perfectly still, his aura so deeply suppressed that even the insects near him continued to chirp. Not even the most gifted of Demon Slayers would have sensed him. His gaze, however, sliced through the darkness like a blade. Closing his eyes, he sensed the world at its purest.
Below him, fleeing through the brush, were the demons.
He felt the presence of five beautiful female demons—each heavily injured, clothes torn and scorched, blood streaking their limbs. Among them were the unmistakable auras of Upper Moon Five, whose breathing was labored but whose movements were still precise and her golden eyes still sharp, Upper Moon Six, younger sister of her counterpart Upper Moon Six, and Upper Moon Eight, smaller in stature but visibly clever in her maneuvers. Trailing close were Lower Moon One and Lower Moon Two, clearly slower, less refined—but still leagues beyond your average demon. Alongside them, surrounding them were three additional demons—not of the Kizuki, but strong. Kokushibo could tell instantly.
And amidst them, shielded within a protective triangle, were two young demons, Kokushibo felt Muzan's slightly distinctive aura from them.
The daughters of Muzan.
Kokushibo had not met any other demon for the past 40 years as he always did his work of hunting and completeing missions to grow stronger alone before returning to his sanctuary. Even before that, ever since he had become a demon, most demons had only heard of his notoriety but had never caught a glimpse. Apart from Upper Moon 2,3,4,7 and Nakime alongside some of the deceased former kizukis, none had seen him as he avoided meeting troublesome people.
Then it happened.
The air shifted. Birds stopped singing. Even the insects went still.
From the surrounding woods, the trees began to shake—not with wind, but with the march of human feet. The ground vibrated. Then came the scent—steel, sweat, and fury.
From every angle, the clearing was flooded with Demon Slayers—a hundred of them, surrounding the demonesses like a tightening noose. And at their center, radiating immense killing intent like twin storms—two current Hashira. Behind them, in perfect formation, were eight former Hashira, retired in title only, their movements still sharpened by decades of war.
The pressure was staggering.
The air thickened, warping like a mirage. The very wind struggled to pass through the clash of intent. It was no longer a battlefield. It was an execution ground.
The female demons froze.
Some staggered back. Others trembled, their bodies instinctively recoiling as their ancient predator—the Slayer Corps—closed in.
One of them, likely the youngest, whispered in a panic, "There's… there's too many…"
Upper Moon Five clenched her jaw, stepping forward, shielding the demon princesses with her body.
Her beautiful ethereal golden eyes scanned the enemies, calculating. But Kokushibo saw it—doubt.
Even she knew.
Ten Hashira. One hundred elite slayers. No escape.
A single voice broke the silence, deep and absolute. It belonged to one of the present Hashira—a man with a blade drawn and burning like hellfire. His voice rang out across the woods.
"Demons, You will all die here today." spoke the said Hashira.
Kokushibo appeared wordlessly at the cliff edge overlooking the battle.
His form shifted through the fog like a phantom, his robes trailing behind him like windblown smoke. Not a sound escaped his steps, not a single leaf stirred to betray him. He moved with unnatural speed and elegance, covering miles in moments, his many eyes scanning the land with supernatural precision. In the blink of the eye he went from the entrance of the forest to the other side where the moutains connected and the battle went on.
The tension reached its peak.
Blades glinted. Fangs bared. Shadows twisted.
And in the darkness above, Kokushibo remained still, unseen by all.
He did not reveal himself. Not yet.
But soon, the moon himself would take action which would turn the forest crimson.