Lily Someya is a first-year student at Sainotama Girls' High School with Austrian and Japanese heritage, reflected in her light green hair, blue eyes, and 164 cm stature. She possesses a severe aversion to men, reacting with immediate physical symptoms like hives upon contact. This reaction also occurs with the female student Nozomu "Baka" Tanaka for unexplained reasons.

Her narrative role frequently parodies lesbian character tropes. Lily openly identifies as a "fan of girls," displaying romantic or physically affectionate behavior towards female classmates. This includes making advances on Saku "Loli" Momoi during gym class, such as groping Momoi's breasts, and nearly kissing Kanade "Majime" Ninomae. Ninomae is the sole character capable of visibly embarrassing Lily. Despite her popularity and beauty, Lily's interactions are complicated by peer eccentricities and her own tendencies.

Lily's nickname connects to lilies and the Japanese word "yuri," denoting both the flower and lesbian themes in media. She maintains a friendly relationship with Kaede, while simultaneously feeling jealous of her. Her core traits and interactions remain consistent across all adaptations, including the live-action drama, manga, and anime, with no documented substantial character evolution or detailed background beyond these established elements.