Kokushibo

Kokushibo is a former Sengoku era samurai, Michikatsu Tsugikuni, and the older twin brother of the first demon slayer, Yoriichi Tsugikuni.

Obsessed with leaving a mark on history and becoming stronger, driven by envy of his brother's talent, he accepted Muzan's offer to become a demon to gain immortality and power. In exchange, he became Muzan's loyal servant and the No. 1 Upper Moon, but throughout his long life he suffered from the realization that he had betrayed humanity and was never able to surpass his brother.

A six-eyed samurai with long red-black hair, patterned clothing, and a giant bone blade.

A majestic, calm and tragic warrior, obsessed with a goal, but maintaining a code of honor.