Kokushibo

Kokushibo is a pale—skinned, tall and muscular man with long pointed black hair with red tips gathered in a ponytail. His most notable feature is the three pairs of eyes on his face with yellow irises and red sclera, which have black straight cracks radiating from each iris. In his middle set of eyes, there are kanji "Highest Rank (? ??, J???)" and "One (???, Ichi?)". Kokushibo also has red markings resembling flames in the upper left part of the forehead and in the lower right part of the chin. A pillar of fog, Muichiro Tokito described its appearance as extremely majestic.[5]
Kokushibo is wearing a purple and black nagagi beehive kimono and a black Umanori-style hakama with a white Uwa-obi. On his belt he wears a sword made of flesh with eyes in between Tsuka tsuka ito. It was later revealed that tsuba and the blade have eyes and veins.age 480, height 190 cm

Little is known about Kokushibo, as he is very secretive.
If we evaluate his behavior at the meeting of the Higher Moons, we can assume that he is punctual and takes his work seriously. Kokushibo demonstrates a strong sense of devotion to the Kibutsuji Mudzan and most of the actions of the First Supreme Moon are dictated by the desire to be more useful in achieving the goals of their leader.
Kokushibo is a man of few words, and although he chooses his words carefully, sometimes they sound rude because of the terrible straightforwardness. Therefore, his threats sound especially frightening.
Later, we see the more humane side of Kokushibo's personality: in memories of his family and brother, he is emotional, he is not alien to experiences, and in a fight with Muichiro, Tokito recognizes his descendant in him and positively evaluates his skill, eventually offering to become a demon.

The main secondary antagonist is (黒死牟 Kokushibo) —the Blade that Cleaves demons: Kimetsu no Yaiba and the First Supreme Moon (上じょう弦げんの壱いち, Jōgen no Ichi?)
Almost five centuries ago in the Sengoku Period, during the Golden Age of the Demon Slayers, Kokushibo was a man named Michikatsu Tsugikuni (継つぎ国くに 巌みち勝かつ, Tsugikuni Michikatsu?)and a former member of the Demon Slayer Corps[2] and the older twin brother of Yoriichi Tsugikuni,[3] the strongest demon slayer who ever lived.
Kokushibo is also the ancestor of Muichiro Tokito and Yuichiro Tokito[4] and is responsible for turning Kaigaku into a demon and joining the Higher Moons.