Marimo Bandō is a second-year student at Kameido High School and a member of its tennis club. Hailing from Japan's Kansai region, she occasionally uses its distinctive dialect. Her personality is defined by unpredictability, eccentricity, and a tendency toward perverse actions, often stemming from significant misconceptions about the world. These misunderstandings frequently lead her into troublesome or harmful situations, ranging from consuming female undergarments to impulsive acts like kidnapping a child.

Despite this chaotic nature, she possesses an underlying kindness. Her immaturity and lack of self-control consistently make her a source of disruption within the group. However, in the absence of other club members—particularly Yuri Oshimoto or Nasuno Takamiya—she can occasionally become the voice of reason, demonstrating situational awareness.

Her life intersects with Tomarin, an extraterrestrial whose spaceship crash-landed on Earth after running out of fuel. Marimo encountered Tomarin following the crash, and the two became roommates and close friends. Their interactions amplify each other's misconceptions; Marimo's distorted views combine with Tomarin's unfamiliarity with Earth, leading to mutual reinforcement of their misunderstandings.

Information regarding Marimo Bandō's background, family history, or explicit character development across the series, its seasons, OVAs, or related spin-off media like *Usakame* is unavailable. Her role remains consistent as a catalyst for comedic conflict and absurd scenarios within the tennis club.