Mana Kuzumi, the 12-year-old sister of protagonist Hiroshi Kuzumi, possesses long black hair, purple eyes, and stands 1.38 meters tall, weighing 36 kilograms. She typically wears a white dress with a bow, a white hat, and white shoes. Following a car accident, Mana relies on a wheelchair for mobility. She has largely adapted to this condition and actively strives for independence, often expressing annoyance when Hiroshi assists with minor tasks she believes she can manage herself, creating recurring friction between them despite underlying care.

Mana exhibits tsundere tendencies toward her brother, occasionally teasing him about romantic interests, particularly neighbor Isuzu Tsumuhana, while simultaneously expressing admiration for Isuzu's older brother, Issei. When confronted about her feelings, she typically responds with silence or sulking. Socially, Mana maintains limited connections outside her family, rarely leaving home and lacking friends her own age. She does develop meaningful bonds with neighbor Isuzu Tsumuhana and classmate Nemuru Kushinada; her friendship with Nemuru began when Nemuru prevented her from falling and gifted her an Usaeru plush toy, which Mana regularly carries during outings.

Mana's personal interests include taking music lessons under teacher Kaori Mana. Her emotional state visibly improves during interactions with Issei Tsumuhana, though she avoids openly discussing these feelings. Mana maintains a generally reserved disposition.