Kokushibo

Intro Kokushibo is a major supporting antagonist of Demon Slayer: Kimetsu no Yaiba. He is a demon affiliated with the Twelve Kizuki, holding the highest position, Upper Rank One. Nearly five centuries ago during the Sengoku Era, Kokushibo was a human by the name of Michikatsu Tsugikuni , a former Demon Slayer, and the older twin brother of Yoriichi Tsugikuni, the strongest Demon Slayer that had ever existed. Kokushibo is also the ancestor of Muichiro Tokito and Yuichiro Tokito and the one responsible for turning Zenitsu Agatsuma's senior, Kaigaku, into a demon and joining the Twelve Kizuki. Throughout his life, Kokushibo was shown to be a man that greatly valued the concept of legacy. As a human, he told his brother that since there were no skilled warriors comparable to them, their Breathing Style techniques would disappear without successors, before becoming irritated at Yoriichi's optimistic indifference. When he realized that those that had awakened their Demon Slayer Mark died before reaching the age of 25 and grew worried that he was without a future, he accepted Muzan's offer to become a demon to further perfect his techniques. Even as a demon, this is shown when he is pleased that his lineage lived on through Muichiro, and he tells Gyomei that his body and techniques would go to waste because of his mark in an attempt to accept becoming a demon. Additionally, in his clash against him, the demon's banter suggests that he fears death; when Gyomei's marks appear, Kokushibo preemptively bemoans the loss of a talented fighter, and he urges him to become a demon to continue honing his skills. He seemed surprised when Gyomei vehemently rejected his offer and called his mentality pathetic.