He is the former instructor of Karma Akabane in his second year as a student of Kunugigaoka Junior High School.

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Oono, much like the other main building staff of Kunugigaoka Junior High School, is very discriminatory and overtly hostile toward the students of Class 3-E. He is a contemptuous individual, who frequently looks down on those he considers inferior. He is also detestable, as indicated when he purposely disrupts the concentration of Class 3-E's students during midterm exams.

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Oono is emphatically concerned with how he is held in estimation by other people. He was initially fond of Karma Akabane because of his good grades, but later forsakes him when he believes that Karma is damaging his reputation.

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