Demon Slayer: Why Michikatsu betrayed his brother and joined Muzan, explained

Michikatsu is an uncommon name among Demon Slayer fans who have only watched the anime. It is a character that was explored in the manga in his human form before he became one of the strongest demons in existence.

The character has deep-rooted ties with another legendary swordsman, Yoriichi Tsukiguni, who nearly beat Muzan single-handedly. Fans who have read the manga are aware of this character’s feats and his reason for becoming a demon.

It also became one of the primary antagonists in the Infinity Castle arc of Demon Slayer. Let us understand his true identity, the reason for betraying his brother, and his abilities as a demon.

Disclaimer: This article contains massive spoilers from the Demon Slayer manga.

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Demon Slayer: Looking at Michikatsu’s life as a human and the events that led to his transformation as a demon

Michikatsu Tsukiguni is none other than Kokushibo, the Upper Moon 1 demon who created Breath of the Moon. Michikatsu Tsukiguni was Yoriichi Tsukiguni’s twin brother. In the Sengoku era, twins were considered bad omens. Yoriichi was sent to a temple because his father found the mark on his forehead to be ominous.

Michikatsu resolved to become a samurai and spent his days perfecting his swordsmanship. However, he was shocked by his brother’s skills with a sword, despite not having practiced as much as he did. But Yoriichi didn’t enjoy combat and swore never to become a samurai. All of this changed when Yoriichi was able to perceive the flow of blood, bone alignment, and muscle contraction when he breathed deeply.

This breathing technique later became the Breath of the Sun, and Michikatsu was shocked that the bodies were transparent to his brother. This only fueled Michikatsu’s desire to become a stronger swordsman. One fateful day, their mother passed away due to an illness.

Michikatsu was worried that Yoriichi would replace him and that he would have to go to the temple in Yoriichi’s place. Yoriichi realized this and bid farewell to Michikatsu before he departed to the temple. His attitude only amplified the resentment Michikatsu only increased from then on.

He went on to marry a woman and became a samurai. Michikatsu led a wonderful life until a demon killed his camp. Yoriichi slayed the demon and apologized for not being able to help earlier. Michikatsu abandoned his family to become a demon hunter. His hatred grew further because he wasn’t able to surpass his brother despite creating his own breathing technique. Kibutsuji Muzan, the prime antagonist of Demon Slayer, convinced Michikatsu to become a demon.

Muzan convincing Michikatsu to become a demon (Image via Koyoharu Gotouge/Shueisha)

He took on the name Kokushibo and became the strongest Upper Moon demon. This transformation took about three days since he was a human being who derived a breathing technique. Following this, Kokushibo killed Oyakata, who led that particular era’s Demon Slayers. Not only did he kill Oyakata, but also got his head to Kibutsuji Muzan. The Demon King’s near-death experience led to the duo killing every single demon hunter except Yoriichi, who used Breath of the Sun.

This is Michikatsu’s story and how he became one of the most terrifying demons to ever exist.