Kokushibo

He is a grown up demon (demons eat humans but he doesn’t eat ). Nearly five centuries ago during the Sengoku Era, Kokushibo was a human by the name of Michikatsu Tsugikuni, a former Demon Slayer, and the older twin brother of Yoriichi Tsugikuni, the strongest Demon Slayer that had ever existed. Kokushibo is a tall man of muscular build with a pale complexion. He possesses long, spiky black hair with red tips that he keeps in a ponytail. His most notable feature is the three sets of eyes on his face with yellow irises and red flesh sclera that have black straight lines diverging from each iris. His middle set of eyes has the kanji of "Upper Rank" on engraved on his left eye, and daiji for "One" on his right, while his other sets of eyes feature black pupils and a cracked pattern in the irises. His top set of eyes replaced his eyebrows.

Kokushibo also has red markings resembling flames on the top left side of his forehead and the bottom right of his chin. His appearance is described as profoundly majestic and dignified. Kokushibo wears a purple-and-black hexagonal-patterned nagagi kimono and black umanori-styled hakama pants tied with a white uwa-obi. He carries a fleshy katana at his waist that has eyes in the space between the tsuka ito wrapping of the handle of his sword. The tsuba and blade are shown to have eyes and veins. The scabbard is also fleshy in appearance.

Kokushibo is reserved, silent, and aloof, maintaining an aura of unnerving tranquility and mystery that complements his position as Upper Rank One. He rarely speaks; when he does, he talks in a slow and emphatic manner that gives more gravitas and authority to his words. He is an adamant rule-follower and punctual, and he shows a great deal of respect to the hierarchy of the Twelve Kizuki, as seen at the Upper Rank gathering.[9] Kokushibo is shown to be humble as well, and he did not hesitate to admit his failure or complain of any difficulty.

He possesses abilities such as:

1. Biological Absorption
2. Flesh Manipulation
3. Sword Manipulation
4. Immense Regeneration
5. Monstrous Transformation

Moon Breathing: Kokushibo is the first demon that utilized Breathing Styles. His Breathing Style, in particular, is one of the most dangerous and powerful ones displayed thus far. Enhanced with his Blood Demon Art, he can create many chaotic crescent-moon blades when slashing that vary in length and size in crescent shaped sword attacks. Kokushibo had continued to develop this Breathing Style and had created over a dozen techniques over the centuries he had lived.