The day had been quiet—eerily so. The kind of silence that hangs in the air before a storm tears the world apart. As night began to fall over the hidden mansion of the Hashira, Tharion sat in silence upon the roof beams, his mask reflecting only fragments of moonlight. He listened to the steady rhythm of swords clashing below, the harsh training of Tanjiro, Zenitsu, and Inosuke echoing through the secluded grounds.
It was then that the voice of the system resonated in his mind.
[System Notification: Tonight, the decisive attack will commence on the hidden Hashira base.][Objective: Survive. Eliminate. Fulfill the final mission.]
Tharion's crimson gaze beneath the mask flickered. His gloved hand tightened around the hilt of his blade, and for the first time in weeks, his breath drew heavy with anticipation.
"So… it begins at last," he muttered under his breath, his voice a low growl. "Finally, I can finish this. Complete the mission. And go home."
The night deepened. Shadows seemed to stretch unnaturally, the mansion wrapped in a veil of quiet that concealed what lurked just beyond the treeline. The crickets ceased their song. The wind stilled. A dread presence drew nearer—like poison spreading in the veins of the world itself.
And then… he came.
Muzan Kibutsuji.
The Demon King himself strode forward with deliberate grace, his aura suffocating, each step dragging the weight of centuries behind it. His eyes gleamed with malice, yet narrowed with sharp purpose. He was not here for blood alone—he was here for the master of the Demon Slayer Corps.
The great doors of Kagaya Ubuyashiki's chamber slid open with a soft groan. Muzan stepped inside, prepared to gaze upon the fragile man he had long considered an insect, a cursed lineage gnawing at him across generations.
But instead of weakness, he found resistance.
Four figures stood in the dim glow of lanterns. Their presences did not waver, their silhouettes etched against the light like unyielding guardians.
Three he recognized instantly—the most formidable warriors of the Corps. Their very existence was an affront to him, the thorns at his side.
Gyomei Himejima, the Stone Hashira, a towering monolith with his chained flail resting silently in his grip.Sanemi Shinazugawa, the Wind Hashira, his eyes burning with fury as sharp as the jagged scars crossing his face.Giyu Tomioka, the Water Hashira, still as a blade drawn under moonlight, his silence more threatening than words could ever be.
But the fourth…
Muzan's gaze froze on the last figure. Cloaked in a long coat of deep black, his face hidden behind a mask unlike any demon or slayer Muzan had encountered before. The air bent strangely around him, his presence unnatural, a ripple of something foreign—something not of this world.
The masked man tilted his head slightly, his voice echoing with calm disdain.
"Tell me, Muzan… is Akaza alright?"
Muzan's eyes narrowed.
"What?" he hissed.
The figure stepped forward, the hem of his coat whispering against the floor.
"I heard… someone beat him so hard he was forced to retreat from the battlefield."
The three Hashira tensed, recognizing the veiled taunt for what it was. Muzan, for the briefest moment, felt something he despised: uncertainty.
Because this man—this masked intruder—was not someone he could place in centuries of memory. His scent was foreign. His aura… untraceable. He was not one of the Corps. Nor one of his demons. Yet he stood in defiance, unflinching beneath Muzan's killing intent.
The silence was thick enough to suffocate. Then Muzan's lips curled, exposing fangs in a cold, venomous smile.
"And who… are you supposed to be?" he asked, voice low and dangerous.
The masked man chuckled softly, tilting his head just enough for the lantern light to catch the edge of his blade.
"The one who will end your hunt."
And in that instant, the room trembled—night itself ready to explode into chaos.
The tension inside the master's chamber had sharpened into a knife's edge. Muzan's lips curled in amusement, though his crimson eyes betrayed the hunger of a beast ready to strike. His pale hand stretched subtly behind his back, his aura swelling like a tidal wave.
Tharion's gaze sharpened beneath the mask.
[System Alert: Dimensional distortion detected. Infinity Castle gateway opening.]
"So this is your trick," Tharion muttered, his voice carrying just enough for Muzan to hear.
Muzan's intent was clear. He would not waste precious time here. Instead, he would tear the Hashira, the Corps, and their master into his endless labyrinth—the Infinity Castle—where his power reigned supreme.
But Tharion was no fool. He had been warned.
As the floor beneath them rippled like water, walls beginning to stretch and bend into impossible angles, Tharion's boots slammed against the ground with a thunderous crack. In an instant, he surged forward, closing the distance with Muzan before the King of Demons could complete his silent command.
His gloved hand seized Muzan's throat, the force shaking the air like a quake. With his other hand, Tharion slammed a seal—etched with unnatural runes foreign to this world—against Muzan's chest.
The Demon King's eyes widened, fury igniting as the seal burned into him.
[System: Seal Protocol activated. Target restricted from exiting dimensional domain.]
"If you want to drag us into your castle," Tharion growled, slamming Muzan bodily through the doorway as the Infinity Castle fully unfolded around them, "then you're staying here too."
With a violent crash, Muzan's body struck the wall of the vast, endless structure, fragments of black wood and stone splintering outward. The castle roared to life—endless stairways spiraling in all directions, shifting platforms rising and falling like the beating of a heart.
One by one, the Hashira fell through the rift, landing on the flat surface of the castle's vast central platform. Tanjiro, Zenitsu, Inosuke, and Nezuko tumbled down after them, catching themselves on the ground. Above them, the chamber stretched on forever, lanterns flickering with sickly red light.
The floor shuddered.
A deafening roar rolled through the chamber as the space filled with shadows.
Then they came.
Thousands of demons—an endless sea of snarling fangs and claws—materialized across the platforms and stairs, their eyes glowing like wildfire. The horde pressed inward, surrounding the Demon Slayers on every side.
And at the far end of the chamber, sitting in ominous silence, stood the figures that made even the bravest hearts falter.
The Upper Moons.
Their presence radiated suffocating menace, their auras crashing over the battlefield like waves of bloodlust.
Yet… something was wrong.
Tharion's eyes narrowed. The Twelve Kizuki stood assembled, but not all of them. The seats of those already slain—Rui, Enmu, Gyutaro, Daki, and Gyokko—remained empty.
The others, however, waited like predators in the dark. Akaza. Kokushibo. Douma. Hantengu. And more. Each one locked their gaze on the intruders, their expressions twisting with anticipation.
Tanjiro's breath hitched, the sheer weight of their enemies threatening to crush him before blades were even drawn. Nezuko growled low, her fangs bared.
But Tharion did not falter.
He stood at the forefront, hand still gripping Muzan's throat as he dragged him off the wall and threw him to the ground before the gathered Hashira. His voice, low and unyielding, echoed through the chamber.
"This is it. The night ends here."
The Infinity Castle trembled in response, its endless corridors alive with the promise of carnage.