Kokushibo

Kokushibo is one of the main antagonists in Demon Slayer: Kimetsu no Yaiba and a member of the Twelve Kizuki, holding the rank of Upper Rank One - the strongest among them. Basic Overview: Real name: Michikatsu Tsugikuni. Affiliation: Twelve Kizuki (serves Muzan Kibutsuji). Age as Demon: Chronologically over 480 years old. Physical Age: Appears in his early 20s to mid-20s, having been turned around age 24. Role: Elite demon warrior. Appearance: Distinctive with six eyes and long dark hair, giving him a very intimidating presence. Backstory: Kokushibo was originally a human samurai from the Sengoku era and the twin brother of Yoriichi Tsugikuni, the most powerful Demon Slayer in history. Despite being skilled, he lived in his brother's shadow and became consumed by jealousy. Fearing death and desiring greater power, he ultimately chose to become a demon under Muzan, abandoning his humanity. Abilities: Kokushibo is extremely powerful, even among demons: Use a unique sword style called Moon Breathing, derived from Sun Breathing. Possesses incredible regeneration and combat skill. His sword is made from his own flesh and can change shape. His multiple eyes enhance perception and reaction speed. Personality: He's calm, disciplined, and speaks like a noble samurai - but underneath that is deep insecurity and envy, especially toward his brother. Why he stands out: Kokushibo isn't just strong - he represents one of the series’ central themes: the destructive nature of comparison and jealousy, especially when tied to family and legacy.