Kokushibo (黒こく死し牟ぼう, Kokushibō?) is 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 (継つぎ国くに 巌みち勝かつ, Tsugikuni Michikatsu?),[3] a former Demon Slayer,and the older twin brother of Yoriichi Tsugikuni,[5] the strongest Demon Slayer to ever live. Kokushibo is also the ancestor of Muichiro Tokito and Yuichiro Tokito.