Shion Chihara is a blonde-haired, green-eyed university student with a height of 1.77 meters who initially presents as male. His appearance is distinguished by a physical scar and a snaggletooth. Together with his close friend Rui Chihaya, he cultivates a reputation as a womanizing playboy.

This lifestyle leads to a consequential event where a woman, seeking to teach him a lesson, administers a drug that triggers a profound physical transformation. Shion's body becomes outwardly female, adopting a darker skin tone consistent with a kuro-gyaru aesthetic, though his male identity persists.

His friend Rui encounters the transformed Shion and, failing to recognize him, is struck by an immediate romantic attraction. After a period where Shion pretends to be a woman, his identity is ultimately revealed to Rui by the recognition of his distinctive scar. This revelation does not diminish Rui's feelings, and the two agree to become secret sexual partners, concealing the transformation from others.

Their relationship evolves into a complex dynamic that navigates themes of identity and attraction. This situation is further complicated by the arrival of Mayu Uehara, who develops a romantic interest in Rui. A doctor and acquaintance of Rui's named Hajime Tsuzuki, who possesses specialized knowledge of the human body, also becomes involved.