Kokushibo (黒こく死し牟ぼう, 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 (上じょう弦げんの壱いち, Jōgen no Ichi?). During the Sengoku Era nearly five centuries ago, Kokushibo was a human by the name of Michikatsu Tsugikuni (継つぎ国くに 巌みち勝かつ, Tsugikuni Michikatsu?), a former Demon Slayer, and the older twin brother of Yoriichi Tsugikuni, the strongest Demon Slayer that had ever existed