Mizuki Mukubayashi is a second-year high school student and a supporting character in the story. She is a classmate of Akihito Abikura, having known him since elementary school, though they were not particularly close during those younger years. With a bright, highly social gyaru personality and a twin side-up hairstyle, she stands out as a confident and energetic presence. She possesses extraordinary athletic ability and is considered one of the strongest girls in her class, holding a position at the top of the social hierarchy. Her strong sense of justice and protective nature make her highly reliable to her friends, as she cannot stand to leave anyone in trouble. This sense of duty extends especially to her homeroom teacher, Hiyori Hiwamura, whom she perceives as innocent and in need of protection. However, she is tough and less kind toward Akihito, viewing him with suspicion for what she sees as taking advantage of Hiyori’s naiveté. Her sharp instincts and assertive attitude drive much of the story’s comedy while she watches over her peers. Her relationship with Akihito carries an undercurrent of long familiarity, but her wariness toward his motives prevents them from being close. Over the course of the narrative, she remains a fiercely loyal friend and a stabilizing force within the class, never hesitating to act when she believes someone is being wronged.