"Ahhhhh!"
A guttural roar tore from Kokushibo's throat. It was a shriek of rage, shock, and centuries of pent-up agony, his entire demonic aura erupting in a violent wave. The man standing before him was not just another Demon Slayer. It was Yoriichi Tsugikuni—his twin brother, the sun he had spent his entire life chasing.
In that single, breathtaking moment, a lifetime of memories crashed down on him.
He remembered a frail, quiet boy who was always gentle. A younger brother who seemed to need protection. But that was a lie. Every choice Yoriichi made, from developing his swordsmanship to protecting their mother, was done with a quiet strength that Michikatsu could never comprehend. He, the older brother, the one who was supposed to be the family heir, had always been consumed by a bitter envy. He saw himself as the gifted one, yet it was always he who was holding them back.
That jealousy festered until they grew older. Yoriichi chose to run away from home, abandoning his birthright. Michikatsu knew why. His brother had left so that his own existence wouldn't threaten Michikatsu's future as the head of the family. From the beginning to the end, Yoriichi Tsugikuni had always been the considerate one.
And what had he been?
Years later, after his life was saved from a demon attack, he met Yoriichi again. His long-lost brother was now a member of the Demon Slayer Corps. The man he had tried to forget guided him onto the same path. Michikatsu learned to fight, creating his own Moon Breathing to stand as a rival to Yoriichi's Sun Breathing. He awakened his Slayer Mark and unlocked the Transparent World, walking the exact same path his brother had once forged.
But walking the same path does not make you the same person. It certainly did not mean he could ever surpass Yoriichi Tsugikuni.
Then came the curse. He learned that swordsmen who awakened the Mark were doomed to die before the age of twenty-five. He was faced with an insurmountable gap between himself and his brother, a finish line he could never reach, no matter how hard he trained. And so, consumed by fear and envy, becoming a demon—an immortal monster—became his last and only choice.
With a thunderous crash, the battle began. Yoriichi Tsugikuni, a legend returned to the world, clashed with Michikatsu Tsugikuni, the man who had abandoned his name to become the demon Kokushibo. The searing light of Sun Breathing met the cold, sharp arcs of Moon Breathing. A ferocious killing aura exploded from both of them, and the sheer force of their peak confrontation sent terrifying shockwaves through the Infinity Castle, tearing the very fabric of the warped dimension apart.
Not far from the duel, the Head of the Priest Clan watched from behind her veil, her eyes glowing with an inscrutable light.
Hmph. Kibutsuji Muzan, you have your schemes, but you are not the only one, she thought, a cold sneer forming on her lips. You think you have trapped us in your fortress, but you have merely given our clan the opening we needed to infiltrate the Japanese Imperial Family.
To the outside world, the conflict was simple: the Demon Slayer Corps, led by the Ubuyashiki family, fought against the demons led by Muzan. But the truth was far more complex. The Priest Clan stood behind the Ubuyashiki, and Muzan himself was nothing more than a failed experiment they had created long ago. They were a splinter faction of the ancient Onmyoji, and now the orthodox line had embedded itself within the Imperial Family of the new Taisho Era—an era where firearms were replacing swords and a constitutional monarchy ruled instead of a shogunate.
In such a modern world, it would have been nearly impossible for the Priest Clan to reclaim their ancient power. But Muzan's renewed war had given them the perfect opportunity. In times of chaos, people look for a savior. It didn't matter if the Priest Clan had started the chaos themselves. If they could eliminate Muzan now, they could seize control and emerge as the heroes who ended it all, reversing centuries of being pushed into the shadows of Japanese history. To achieve that, however, taking down Kibutsuji Muzan was an absolute necessity.
The explosive battle between the brothers paused for a breath. The figures of Yoriichi and Kokushibo separated in mid-air, a tense silence hanging between them. It was clear to both that neither could easily kill the other.
"So many years have passed, and you're still the same…" Kokushibo hissed, all six of his eyes fixed on Yoriichi. His killing intent surged, fueled by the same toxic envy that had defined his human life. As a demon, those feelings had only sharpened into something monstrous.
But before their fight could resume, the space between them shimmered. Countless motes of dark light appeared, and the air plunged into a frigid cold. Two figures emerged from the distortion, and their presence sent a shockwave of disbelief through both Yoriichi and Kokushibo.
Stepping out of the portal were Kagaya Ubuyashiki and his wife, Amane, their bodies twisted and transformed into those of powerful demons. Their faces were hauntingly familiar, but their auras were utterly alien, reeking of corruption and blood.
"Clan Head… we have returned!" Kagaya's voice echoed, no longer gentle or soothing, but sharp and laced with malice. "All the suffering the Ubuyashiki Clan endured for centuries will be repaid today!"
His cold eyes locked onto the Priest Clan Head. "Your precious Guardian Priests have already been slaughtered by our hand!"
As he spoke, several round objects were thrown from the portal, thudding heavily onto the ground. They were the severed heads of the Clan Head's personal bodyguards. These priests were the elite of their clan, warriors whose skills were said to rival those of the Twelve Kizuki or the Hashira. And in a matter of moments, they had been annihilated by the demonized Kagaya Ubuyashiki.
It was horrifyingly clear that Kagaya was not merely corrupted. He was completely lost. For the man who had once valued life above all else, it no longer held any meaning at all.
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