Mari is a college student and tennis club member, becoming the focus of Hiroshi Karigari's unrequited affection. She possesses distinctive blue hair, a deliberate visual contrast to the pink hair of the android Marie later created in her image. Her initial interactions with Hiroshi are limited due to his social awkwardness, confined to routine encounters at the tennis club where he performs ball-retrieving duties.

The plot escalates when Hiroshi's duplicate android, Marie, meets Mari. To conceal Marie's origin, Hiroshi claims she is his sister, an explanation Mari accepts without question. She forms a friendship with Marie, treating her solely as a striking look-alike acquaintance. Mari remains entirely unaware of the central conflict involving Hiroshi, the android Marie, and the delinquent Hibiki Kennou, who blackmails Hiroshi by threatening to expose Marie. She is equally oblivious to Hibiki's aggressive pursuit of Hiroshi.

The narrative provides no exploration of Mari's reactions to these events, nor does it delve into her personal background, family life, or future aspirations. The OVA's third episode shifts its focus to android Marie's dream sequences, leaving Mari's character without further development, resolution, or involvement in later plot points. Her relationship with Hiroshi concludes without romantic reciprocation or substantive closure. Mari does not appear in any spin-offs, films, or extended media, and information regarding her life beyond college, hobbies, or relationships outside the tennis club setting is absent.