Tamaki Saimon is a twelfth-grade student and childhood friend of Rouma Oriya, known for her carefree, friendly, and deredere personality. She possesses brown waist-length straight hair typically tied in a ponytail, garnet-colored tareme eyes, and a slim teenage build standing 162 cm tall with measurements of 84-59-80 cm (C cup). Her common wardrobe features school uniforms, thigh-high stockings, miniskirts, sweaters, tank tops, and an apron from her part-time waitressing job.

Serving as manager of the school's kickboxing club, Tamaki actively recruits members like the mysterious Kishida and persistently hounds Rouma to attend practices, showing deep concern for his activities. Their long-standing relationship is marked by frequent arguments and a love-hate dynamic. Tamaki exhibits jealousy when Rouma interacts with girls like Yuuri Shirai and displays possessiveness, including stalking him across town and confronting him about his whereabouts, despite publicly downplaying their connection.

Tamaki maintains a confirmed romantic relationship with an unnamed medical student. Concurrently, she shares a sexual relationship with Rouma devoid of formal romantic commitment. This arrangement shatters when Tamaki discovers Rouma neglected contraception, prompting her to angrily terminate their physical involvement. The fallout leads to cold interactions despite shared club duties, though Tamaki later attempts reconciliation.

Her background involves childhood flashbacks featuring the transfer student Kishida, including a traumatic alleyway assault by thugs. While initially crediting Kishida for her rescue, Tamaki later learns Sukekiyo Koudaiji intervened. She faces significant challenges managing the kickboxing club, including budget cuts and potential disbandment, intensifying her recruitment efforts.