Hattori was one of the senior members of the karate club, until Masaru defeated the whole club single-handed, leading to its disbanding. To add to his anger, Masaru nicknames him "Umaibou" (a 10-yen snack). Bent on extracting his revenge, he repeatedly tries (and fails) to defeat Masaru in combat. He is normally seen in casual clothes rather than the school uniform, even though he is supposed to be a student.
