Demon Slayer: Why Did Kokushibo Become A Demon?

Pavas Gagneja
Aug 28
3 min read

SPOILER ALERT: This article may contain major spoilers from Demon Slayer. Proceed only if you don't mind having key story elements revealed.

Long before Kokushibo became Upper Rank One, he was Michikatsu Tsugikuni, the older twin of the legendary Yoriichi Tsugikuni, who became a Demon. Michikatsu was a gifted warrior, but his strength felt insufficient next to Yoriichi’s overwhelming talent.

Is that the reason why Kokushibo turned down a dark path and decided to become a Demon? Or was there something else? There's a lot we still don't know about this character. But one thing is for sure: jealousy wasn't the only reason for this decision. Let's decode what Kokushibo's motivations were.

ALSO READ: Demon Slayer: Why Did Akaza Choose To Die?

Living In Yoriichi’s Shadow

Kokushibo and Yorrichi meet after the former turned into a Demon

Michikatsu’s life was defined by comparison. Yoriichi was self-sufficient, while Michikatsu wasn't. Every milestone Michikatsu achieved as a human swordsman was undermined by his brother’s natural grace and Sun Breathing’s perfection.

But the admiration turned into quiet resentment, and respect was poisoned by shame. Even as a skilled warrior, Michikatsu felt like a side character in his brother's life. And that pain grew instead of fading.

When Michikatsu awakened a Demon Slayer Mark, he thought he could finally take the spotlight. But the Demon Slayer Mark’s curse meant his peak would be short-lived. As a result, accepting Muzan’s blood seemed like the only way to keep going on, even if it meant changing what he was.

The Bargain: Immortality For Integrity

Choosing to become a Demon gave Michikatsu a new name, Kokushibo. Along with that, it gave him an endless future, at the cost of his soul. He gained immortality, monstrous strength, and a Demon’s regeneration; he even molded his own flesh into a living blade and adapted Moon Breathing into a terrifying counterpart to his brother’s style. By every measure of battle, he became extraordinary.

However, his power multiplied his insecurity rather than curing it. Immortality preserved his envy. As a result, this trapped him in a cycle of chasing a man he could never surpass. The longer he lived, the more he realized that perfection can’t be stolen — it must be owned.

Moon Breathing And Mastery Without Peace

Kokushibo’s Moon Breathing looks amazing — shining arcs, many blades, and attacks from unexpected angles. But behind its beauty is pain. Sun Breathing comes from peace, while Moon Breathing was created from jealousy and fear. It is a sign of Kokushibo’s talent and a reminder of his sadness.

He made techniques that almost no one else could match and honed them for centuries. But every improvement reminded him of what he lacked. Even though he was powerful, respected, and feared, he was always in the shadow of the Sun.

The Fear Behind The Choice

Kokushibo appears in the Infinity Castle

Kokushibo was also driven by fear. It was the fear of dying unfulfilled, the fear of being second forever, and the fear that his best wasn’t enough. Muzan’s offer didn’t just tempt his pride; it fed into his fear of time. As a Demon, he could keep training, keep perfecting, keep trying.

He wanted greatness so much that he lost the part of himself that could have actually found it. So he accepted Muzan's offer because it seemed like the only choice he had to become the best. However, it wasn't.

In the end, Kokushibo became a Demon to outrun death and surpass his brother. Eventually, he found neither. His story is a quiet warning: if the goal is built on fear and envy, even immortality won’t be long enough. The only victory that lasts is the one made with acceptance — something Kokushibo could never make his way into.