Mitsuru Kokubo is a third-year student and defender for Seiseki High School's soccer team, originally from Kanagawa Prefecture. He is known for his flirtatious and laid-back personality, often engaging in casual relationships with multiple girls at the same time, a pattern that reflects his general take on life. This carefree attitude also extends to his soccer training, where he tends to maintain a relaxed approach. Kokubo's confidence is a defining trait, though it sometimes tips into overconfidence. On the pitch, he plays as a defender, contributing to the team's defensive line. Off the field, he has a special skill for making candles and enjoys mud packs, while he dislikes heading practice. His motivations are not deeply explored, as he appears content with a casual and unchallenging lifestyle. In the story, he serves as a supporting character, with his romantic entanglements and easygoing demeanor providing recurring side elements. He does not undergo significant personal growth, remaining consistent in his flirtatious and relaxed nature throughout the series. His key relationships are primarily as a teammate, with no close bonds or rivalries particularly emphasized.