Who Is Kokushibo? Upper Moon 1, Michikatsu and Yoriichi Explained
5 October 2026 · 7 min read · by OCpit
Kokushibo is Upper Moon One, the strongest of the Twelve Kizuki and the most powerful demon serving Muzan. As a human he was Michikatsu Tsugikuni, the older twin of Yoriichi, the greatest swordsman Demon Slayer ever shows. Everything about him, the six eyes, the Moon Breathing, the centuries of loyalty to Muzan, comes back to one thing: he could not bear being second to his brother.
Who is Kokushibo?
Kokushibo is a demon swordsman. Unlike almost every other demon, he fights with a katana and a breathing style, Moon Breathing, which he created himself while still human. His sword is grown from his own flesh, so it regenerates like the rest of him. He has three pairs of eyes, and the middle pair carries the kanji for "Upper Rank One".
He is calm, formal and quiet, and he speaks slowly. He has held the top rank for centuries and is the one who turned Kaigaku, Zenitsu's former training partner, into a demon. Anime viewers first see him at the Upper Moon meeting in the Swordsmith Village arc.
His human past: Michikatsu Tsugikuni
Michikatsu and Yoriichi were born twins into a samurai family in the Sengoku era. Twins were considered bad luck, and Yoriichi was born with a birthmark, so their father favoured Michikatsu and planned to get rid of the younger boy. Michikatsu pitied his quiet brother and made him a small flute.
Then Michikatsu saw Yoriichi pick up a practice sword for the first time and effortlessly beat a trained instructor. From that moment, pity turned into envy. Yoriichi left home, and years later the brothers met again when Michikatsu, now a samurai with a wife and children, was saved from a demon by his twin. Michikatsu abandoned his family to join the Demon Slayer Corps and learn Yoriichi's techniques. He could not master Sun Breathing, so he adapted it into his own style: Moon Breathing.
Why he became a demon
Michikatsu awakened the Demon Slayer Mark, which boosts a swordsman's power but kills its bearer young. Facing that curse while still falling short of Yoriichi, he accepted Muzan's offer: become a demon and have all the time in the world to perfect his sword.
Kokushibo traded his humanity, his family and his honour for more time. Five hundred years later, he still had not caught up.
The last meeting with Yoriichi
Decades later, Kokushibo met his brother one final time. Yoriichi was in his eighties, and Kokushibo, still young as a demon, was shaken to find him as strong as ever. Yoriichi was about to land the killing blow when he died of old age, standing, mid-stance. Kokushibo cut the body in half in frustration, and the flute he had made as a child fell from Yoriichi's robes. His brother had carried it his whole life. Kokushibo kept it for the next few centuries.
How Kokushibo dies (major spoilers)
In the Infinity Castle arc, Kokushibo fights Muichiro Tokito first, recognising him as his own descendant. He is then joined by Genya, Sanemi Shinazugawa and Gyomei Himejima, two of the strongest Hashira. Muichiro, badly wounded, drives his sword into Kokushibo and turns it red, which weakens him enough for the others to break through.
To survive, Kokushibo regenerates into a grotesque new body covered in blades. Then he sees his reflection in Sanemi's sword and is horrified at what he has become. He stops fighting the damage, and his body crumbles. All that is left is the flute. Muichiro and Genya both die from their injuries.
Building a demon OC like Kokushibo
- ▹Give them someone to lose to. Kokushibo's whole story is about a rival he could never beat. A demon OC driven by one person is instantly more interesting than one driven by hunger.
- ▹Keep one object. The flute does more work than any fight scene. Give your OC a small thing they cannot throw away.
- ▹Let the power cost something. He kept his sword skills, but lost his face, his family and his name.
Try it in the Demon Slayer OC creator, then read Akaza explained for another Upper Moon whose demon life is shaped by the human he forgot.
As an Amazon Associate, OCpit earns from qualifying purchases.
Kokushibo FAQ
Is Kokushibo stronger than Akaza?
Yes. Upper Moon One sits above Upper Moon Three, and in the manga Kokushibo needs two Hashira plus Muichiro and Genya to bring him down.
Is Kokushibo the strongest demon?
He is the strongest of the Twelve Kizuki. Only Muzan, the source of every demon, is stronger. Next in line is Doma, Upper Moon Two.
Frequently asked
›Who is Kokushibo in Demon Slayer?
Kokushibo is Upper Moon One, the highest ranked of the Twelve Kizuki and the strongest demon below Muzan. As a human he was Michikatsu Tsugikuni, the older twin brother of Yoriichi Tsugikuni, the swordsman who created Sun Breathing.
›What is Kokushibo's human name?
Michikatsu Tsugikuni. He was a samurai in Japan's Sengoku era, around five hundred years before the main story, and later joined the Demon Slayer Corps before becoming a demon.
›Why did Kokushibo become a demon?
Envy and fear of death. He could never match his twin Yoriichi, and after awakening the Demon Slayer Mark he faced the curse that kills its bearers young. Muzan offered him endless time to perfect his swordsmanship, and he accepted.
›How does Kokushibo die?
In the Infinity Castle arc he fights Gyomei, Sanemi, Muichiro and Genya at once. Muichiro turns his blade red inside Kokushibo's body, and when Kokushibo sees his monstrous new form reflected in Sanemi's sword he is horrified, stops regenerating and crumbles away. Only Yoriichi's flute is left.
›Is Kokushibo related to Muichiro Tokito?
Yes. Muichiro is a descendant of Michikatsu's human family, which makes Kokushibo his distant ancestor. Kokushibo recognises this during their fight.
›Who voices Kokushibo?
In Japanese, Kokushibo is voiced by Ryotaro Okiayu, also known as the voice of Byakuya Kuchiki in Bleach.