Chisato Hagiwara is a central figure in her high school story, recognized as the star player and captain of the girls' water polo club. As a second-year student, she is portrayed as a beautiful and hardworking young woman who is deeply dedicated to the sport. Her personality is defined by her serious and responsible nature; she is kind and helpful to her teammates, constantly pushing both herself and the other club members to perform better, a drive born from a history of past defeats. Despite her popularity and having a following of admirers, she remains quite innocent and has no interest in romantic relationships, lacking experience in dealing with love and her own emotions. Her commitment to water polo is so strong that she has an almost obsessive dedication to mastering the sport.

In the narrative, Chisato serves as a key figure who inspires the protagonist, Yōhei Hamaji. Although she initially berates him for his perverted and unmotivated attitude, she is also one of the few girls who genuinely cares about his wellbeing. This complex interaction causes Yōhei to develop a serious crush on her, which in turn motivates him to take water polo seriously for the first time in an effort to win her affection. For her part, Chisato cannot stand the perverted behavior of the boys' team, and she initially has no interest in Yōhei's romantic advances, though his growing dedication to the sport begins to change the dynamic between them.

Regarding her abilities, Chisato is a highly skilled and formidable water polo player. As the captain, she is looked up to by her teammates who rely on her leadership in the pool. Her character is marked by a minor but defining trait of being a bit clumsy, which contrasts with her otherwise sharp and focused athletic persona. Her role and development revolve around navigating the serious demands of competitive sports while slowly coming to terms with the unexpected attention and feelings brought on by her evolving relationship with Yōhei.