Mutsumi Mitsuba, a first-year student at Ōsai Academy who progresses to her second year, balances her role as the judo club’s founder and head with an infectious, energetic charm. Her physical strength and athletic prowess anchor the club’s success, while her buoyant personality makes her a natural social hub, effortlessly connecting with peers. Academics, however, challenge her focus—classes often lull her into drowsiness, and restless energy keeps her from staying seated long.

Long black hair swept into a high ponytail frames her athletic build, praised by her best friend Chiri as “well-proportioned.” A blend of innocence and physical confidence defines her: she mistakes suggestive jokes as literal advice, envisioning risqué banter as wrestling tips, yet executes feats like skating circles around struggling peers with ease.

Her longtime crush on Takatoshi Tsuda drives much of her growth. After recruiting him to help launch the judo club, she openly admires him, inviting playful teasing from Chiri. Though bold in sports, romantic moments fluster her—freezing mid-contact or hastily smoothing her ponytail when he enters a room. Missed opportunities to deepen their bond stem from her obliviousness, like refusing his help to hide sweat or overlooking chances for closeness during group outings.

Close friendships with studious Suzu Hagimura, whom she visits for sleepovers, and confidante Chiri, her judo vice-captain, anchor her social life. She respects figures like Shino and Aria but misreads their humor, taking innuendo at face value. Motion sickness plagues her during team bus rides, sparking frustration, while her traditional dream of becoming a bride underscores her values.

Notable details include her surname (“three leaves”), a blink-and-miss anime cameo, and childhood belief that her parents’ nighttime noises were judo practice. Across media, her self-awareness about her feelings for Takatoshi grows, yet her core innocence and steadfast dedication remain unchanged.