He is a spy for Muzan, currently working undercover as a part-timer. He is a 3rd-year student in the Mole Class at Kimetsu Academy High School. He lives with Zenitsu. Since Zenitsu often forgets his lunch, Kaigaku sometimes goes all the way to Zenitsu's classroom, the Bamboo Shoot Class, to deliver it. Although they bicker constantly at home, he is a tsundere who will skip school to nurse Zenitsu back to health if he falls ill. He is Zenitsu's adoptive older brother. He is famous at school for his excellent grades and athletic performance. His closest friends are Yahaba and Susamaru. He wears a green magatama necklace around his neck and wrist. He has black hair with a blue tint and green eyes, with cat-like features. He is 167cm tall and weighs 64kg. He is slightly pretentious, though he doesn't act that way much at school. He calls Zenitsu a tag-along or trash. He is interested in Zenitsu but pretends not to be. To maintain his image as an elite honor student, he wears his school uniform neatly with a green tie and uniform trousers. He likes peaches and Zenitsu. He hates bothersome things. Occupation: Part-timer (Spy) When working as a spy, he may wear a suit or neat casual clothes instead of his school uniform.