Kokushibo
His true name was Michikatsu Tsugikuni. In the world of Demon Slayer, he was the strongest of the Twelve Kizuki, the elite group serving the progenitor of all demons, Muzan Kibutsuji. Holding the rank of Upper Rank One, he was a creature of peerless power who had never been unseated from his position since the group's inception until its eventual fall. Before his descent into monstrosity, he was a high-ranking member of the Demon Slayer Corps—a Hashira who pioneered the Breath of the Moon in his quest to eradicate the very evil he eventually joined.
But no matter how he bled, toiled, or broke his own bones in effort, he could never surpass his younger brother, Yoriichi Tsugikuni—a genius born blessed by the gods themselves. Driven by a hollow sense of inferiority and jealousy, he succumbed to Muzan's whispers and chose to become a demon.
That is who I am now. I have become Kokushibo, Michikatsu Tsugikuni.
I am a reincarnated soul. In my previous life, I was an otaku who immersed himself in subcultures—anime, manga, and games. Because of that, I didn't panic when I realized I had been reborn; in fact, I rejoiced.
I had been a nobody, a jobless man living day-to-day on part-time shifts, until a hit-and-run ended my miserable life. To be given a second chance as my favorite character was nothing short of a blessing.
In Demon Slayer, I didn't care for the protagonist, Tanjiro Kamado. I admired the pillar of evil, Kokushibo. He had power, intellect, charisma, and an unmistakable aura. To be honest, if Muzan had been even half as impressive as Kokushibo, people wouldn't have mocked him as a coward. Seeing Muzan simply flail tentacles around and release shockwaves still irritates me to this day.
"Sigh... I've lost myself in idle thoughts again. Moon Breathing, First Form: Dark Moon, Evening Palace."
With a wide horizontal sweep, a singular blade path cut through the air, slicing a massive boulder in the training hall as if it were soft tofu.
As expected, Kokushibo's swordsmanship remains intact. Or rather, even if I inherited the potential, I wouldn't have reached this level without my own grueling effort.
"I've held this form and these powers since I was four years old..."
The world I was reborn into was not the world of Demon Slayer, but rather the world of My Hero Academia.
I knew this because, shortly after my birth, I saw my parents using superpowers as if they were perfectly natural. I saw people with mutated bodies and Quirk users on the streets. And on the TV, there was a massive, muscular man with golden tufts of hair and a radiant smile: All Might. That confirmed it.
I had been reincarnated as Michikatsu Tsugikuni in the world of Heroes.
When my Quirk manifested at the age of four, I ceased to be truly human. Marks appeared on my skin, my eyes split into six, and the kanji for 'Upper Rank One' became etched into my irises. My physical capabilities far surpassed those with typical enhancement Quirks. Even if I were wounded or lost a limb, I would simply regenerate. From the moment my Quirk awakened, I had become a Demon.
Curiously, however, I felt no urge to consume human flesh, nor did I possess the lethal weakness to sunlight. My regenerative powers, transcendent physicality, and Blood Demon Arts were all there, but the hunger and the sun's curse were absent. It was strange, but I decided not to question a good thing.
I sheath Kyokuseibo—the sword forged from my own flesh and bone—into my body and took a sip of a sports drink. I can eat and drink human food normally, which is a relief. Even if a demon doesn't feel hunger in the traditional sense, losing the joy of eating would be a tragedy. Is it not one of the three great desires of life?
"Phew... I am not physically tired, but the mental fatigue is real."
"You've worked hard, Brother."
A tall, handsome boy with a stoic expression approached and handed me a towel. This was Yoriichi Tsugikuni. In the original story, he was the source of Kokushibo's inferiority complex—the creator of Sun Breathing and the strongest being in the history of Demon Slayer. He was so terrifyingly powerful that he nearly decapitated Kokushibo even as an old man on the verge of a natural death. He was so formidable that Muzan stayed in hiding until the day Yoriichi finally passed away.
Now, he looked at me and offered a small smile. In this world, he was born as my younger brother, just as in the original.
However, there was one major difference: we are brothers who genuinely love each other.
I have no reason to be jealous of Yoriichi. Our father in this life is not the monster from the original era; he is a man who loves his children. Our mother is healthy, kind, and generous with her affection. This isn't the broken Tsugikuni household of the past; our family bonds are ironclad.
Since I am not the original Michikatsu, I have no reason to envy my gifted brother.
Yoriichi possesses the same monstrous physical stats and his Sun Breathing is a constant, passive state for him. His skill and power are already enough to easily suppress most Pro Heroes, but he has no desire to show it off. He simply dreams of becoming a civil servant and living a quiet life.
If this guy became a Hero, he'd reach the very top in no time...
"Yoriichi, are you certain you won't become a Hero? With your talent, you could easily be among the highest-ranked."
"I have no interest in such things, Brother. I only wish to spend peaceful days with my family. That is my happiness."
"Is that so? If that is your wish, I shall respect it."
I patted Yoriichi's head. He is such a diligent and admirable brother; the original Michikatsu was a fool to be consumed by petty jealousy. I am different from him. Even if he was my favorite character, I can't defend his past actions—he deserved a wake-up call for that.
"Hmm... it will be dinner time soon. While I do not feel hunger, the act of dining is an important matter."
"Mother said we are having Nabe tonight, Brother."
"Is that so? Nabe... that sounds pleasant."
The two of us walked through the Tsugikuni estate toward the dining room. Our family comes from an ancient samurai lineage that has produced many famous generals. We still maintain many old traditions, living in a refined, traditional style. We wear yukatas at home, and our speech remains formal and archaic—especially mine.
"Yoriichi..."
I stopped and looked at my brother with my six eyes.
"Does my current appearance not disturb you? Since I was four, I have changed. I have taken on the visage of a monster. Does it truly not bother you to look upon such a foul and hideous form?"
Ever since my Quirk awakened, I have been the subject of gossip and cold stares. People looked at me as if I were a monster, and I've grown used to being mistaken for a villain.
Because our family is prestigious, no one insulted me to my face, but the subtle bullying, contempt, and discrimination in the shadows often weighed on me.
But my family never treated me like a monster. They never discriminated against me; they treated me exactly as they always had.
"You are my brother," Yoriichi said, offering a gentle smile. "No matter what form you take, you will always be my kind brother."
I reached out and patted his head again.
I am truly happy.