Mutsumi Mitsuba is a vibrant student at Ōsai Academy, progressing from first to second year. As the founding leader of the school's judo club, her dedication and martial arts skill are evident. She possesses notable physical strength, an athletic build, and excellent condition, her long black hair typically secured in a practical ponytail.

Energetic, cheerful, and refreshingly innocent, Mutsumi naturally lifts the mood and befriends classmates easily. This innocence often causes her to misinterpret or completely miss the sexual innuendos directed her way, especially by student council members. Despite her athletic prowess, she finds academics challenging, frequently dozing off in class and struggling to stay seated for long periods.

A significant development involves her burgeoning romantic feelings for her classmate, Takatoshi Tsuda. These feelings trigger visible flustering or physical paralysis during their interactions, starkly contrasting her usual judo confidence. She openly states her ultimate dream is to become a bride, signaling a shift from purely martial arts goals to personal aspirations. Her interactions within the judo club, including her friendship with Chiri Nakazato, and her reactions to Takatoshi illustrate her evolution from a solely club-focused individual navigating complex personal emotions.