Marimo Bandō is a 16-year-old female second-year student at Kameido High School and a member of the Tennis Club. She stands 169 cm tall and weighs 58 kg, with blue hair and blueish-purple eyes, though some sources reference her hair as pink. She is right-handed.

Her numerous misconceptions about the world fuel repeated antics causing trouble or harm to herself and others. Documented incidents include wearing another girl's panties on her face, stealing and consuming girls' panties, and kidnapping a child. These actions have led to news headlines and multiple arrests. Despite this lack of maturity and self-control, she retains a fundamentally kind nature.

Her behavioral patterns remain consistent across all seasons, movies, OVAs, and spin-offs. She sings the fifth season opening theme "Qunka!", which focuses on smelling and eating panties. In episodes and official artwork, she attempts to take another girl's panties while worn, photographs exposed underwear, uses her tennis racket to lift another girl's skirt, and grabs a club member's breasts while claiming police pursuit.

Unexpectedly, despite being the club's most unpredictable member, she occasionally becomes the voice of reason when others are absent. She forms a stable friendship and becomes roommates with Tomarin, an alien who crash-landed on Earth, though Marimo's misconceptions frequently worsen Tomarin's misunderstandings about human society.

Her core traits, behavioral patterns, and role within the Tennis Club remain consistent throughout all appearances, without significant background story or character development.