Kamui is a member of the Yato Tribe, the son of Umibouzu and older brother of Kagura. His excellent fighting skills helped him become Captain of the 7th Division of Harusame's Thunder Guns, the most powerful combat unit within the Harusame group and Overlord of Yoshiwara. Since defecting from the Harusame, he no longer holds these positions. Kamui firmly believes that the Yato are to remain on the battlefield and shows his disapproval of Housen staying locked up in Yoshiwara. Because of this belief, he shows no pity towards family or subordinates as a sign of weakness is unacceptable. He tried to revive the abandoned tradition of Yato clan's men killing their own parent to prove their strength, although failed to successfully execute it and only cut his father's arm off. Despite this, he pays respect to the opponents he kills by sending them off with a smile. He doesn't kill children, and dislikes killing women because they may give birth to strong children.

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Kamui lived with his parents and his younger sister on Rakuyou when he was young. As a child, he took over his mother Kouka's responsibilities in doing the house chores and taking care of the then infant Kagura when Kouka fell ill. He also took up the responsibility to protect his mother and younger sister in the absence of his father Umibouzu, who was seldom around as he was travelling around the universe searching for a cure to Kouka's illness.