Yūki Kagami is a male student accidentally placed in the girls' dormitory at Otorinashi Academy because of a paperwork error involving his gender-ambiguous name. To evade expulsion, he adopts the cross-dressing identity "Kasai Yuki" within the dorm and rooms with his homeroom teacher, Ayana Kakinozaka, who originated the mistake. His naturally feminine appearance and timid demeanor sell the disguise, yet inadvertently draw unwanted attention.

Kagami demonstrates a responsible and well-intentioned character, frequently deflecting romantic or sexual overtures from female students to prevent complications. Despite this, he unintentionally becomes the focal point of a harem as multiple characters develop intense attractions. His hidden identity sparks escalating issues, such as Risa Takabane uncovering his secret and coercing him into servitude in exchange for silence. Patricia Bepouin, the student council president, initially suspects him of wrongdoing but later grows enamored.

A defining characteristic is his sensitivity when the knot of hair atop his head is touched, which provokes arousal. Though generally level-headed, he occasionally reveals subtle perverted inclinations. His relationship with Ayana remains ambiguously close, with her exhibiting increasing jealousy toward other admirers. Childhood friend Kotomi Shirakawa also nurtures affection for him, though he initially fails to recall their shared history.

Throughout ongoing events, Kagami stays predominantly reactive to mounting chaos without fundamental personality shifts. His priority remains guarding his secret while managing demands from enamored girls—particularly Risa's manipulative schemes and Ayana's possessive behavior. The narrative underscores his perpetual misfortune and the farcical tension fueled by his concealed identity.