Movie
Description
Kotomi Tsuda is Takatoshi Tsuda's younger sister. Initially a 14-year-old third-year junior high student, she later becomes a 15-year-old first-year student at Ousai Academy, choosing it for its proximity to home. She has long dark brown hair usually in twin tails, large brown eyes, and a frequent cheerful grin. Her sense of style surpasses her brother's, featuring varied casual outfits. After entering high school, physical development causes discomfort with her initial uniform fit.

Academically lazy and unmotivated, she requires extensive tutoring from Takatoshi or Suzu Hagimura to pass at Ousai. Despite this, she is sociable and popular, easily forming friendships across grades like senior Mutsumi Mitsuba. Her natural charm sparks suggestions of an idol career. Her personality blends childish imagination—like role-playing as a shounen anime protagonist—with a notorious, shameless fascination with adult topics. She exhibits extensive knowledge of dating simulation games (galge) and pornography, frequently making explicit sexual remarks regardless of setting or company. This behavior embarrasses Takatoshi and friend Kaoru Toki, positioning her among the series' most perverted characters alongside Shino Amakusa, Aria Shichijō, and Naruko Yokoshima.

Her relationship with Takatoshi is close and affectionate, marked by reliance due to their parents' frequent absence. She jokes about incestuous feelings, fueled by provocative humor and an airheaded nature, though no concrete evidence supports genuine romantic attraction; these jokes remain ambiguous but consistently part of her comedic persona. Her closest friendship is with Kaoru Toki, whom she helps overcome social awkwardness despite Toki's delinquent appearance. She maintains respectful bonds with student council members: admiring Shino's leadership, interacting comfortably with Aria, and valuing Suzu's academic support. She perceives Shino's feelings for Takatoshi, though her awareness of Suzu's similar affections is less clear.

Across the series, OVAs, and films, Kotomi evolves from middle schooler to active high school participant. Her entrance exam success is implied to result from an interview with Naruko Yokoshima, who recognized a "kindred spirit." At Ousai, she joins the Go Home Club and briefly participates in the Judo Club. She engages in school events like cultural festivals, beach trips, and mixers, often driving comedic situations through uninhibited dialogue. An OVA depicts her in wedding attire during a fantasy sequence about Takatoshi's potential brides, highlighting jokes about their sibling dynamic. Her development retains core traits: academic struggles, sexual humor, and loyalty to friends, without significant romantic progression or resolution of incest-themed gags.