okushibo (Kokushibō?) 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 (Jōgen no Ichi?).
Nearly five centuries ago during the Sengoku Era, Kokushibo was once a human by the name of Michikatsu Tsugikuni (Tsugikuni Michikatsu?), a former Demon Slayer and the older twin brother of Yoriichi Tsugikuni, the strongest Demon Slayer that ever existed.
Kokushibo is also the ancestor of Muichiro Tokito and Yuichiro Tokito[6] and the one responsible for turning Zenitsu Agatsuma’s senior, Kaigaku, into a demon and joining the Twelve Kizuki.