Kokushibo is the Twelve Kizuki, which holds the 12 strongest beings amongst the demon-kind, only inferior to the Demon King himself, Muzan Kinutsuji. Kokushibo was a human five centuries ago, during the Sengoku Era. Under the name of Michikatsu Tsugikuni, he is the ancestor of the current Hashira Muichiro Tokito.

He was also the older twin brother of Yoriichi Tsugikuni, often regarded as the strongest demon slayer and the founder of the breathing styles that the current demon slayers use. He found the first style, Sun Breathing, passed down as Hinogami Kagura and used by Tanjiro. There isn’t much revealed about him in the anime, but the manga defines his personality and history well.Kokushibo is pale-complexed, tall, muscular build. He possesses long, black, spiky hair with red tips tied up in a ponytail. His most noteworthy feature are his three sets of eyes present on his face, and his middle yellow irises consist of the mark of Upper Moon One. Kokushibo dons a purple-and-black hexagonal patterned kimono. His human form resembles his demon form pretty well. The only difference is his three sets of eyes, which are replaced with a single pair of eyes, and he has a white kimono.

Kokushibo is quite reserved and silent. He often keeps to himself while retaining an aura of unnerving tranquility and mystery that adds to his personality as the topmost demon. He rarely speaks, but when he does, his emphatic tone gives him authority over his entire demeanor.