Tsukiko Yahisa is the first and only female student to enroll at Seigetsu Academy, a former boys-only high school dedicated to the study of the stars. As a girl, Tsukiko stands out from the rest of the student body, and her childhood friends—Kanata Nanami and Suzuya Touzuki—devotedly shield her from many difficulties the other boys cause. On the outside, the arrangement between the three of them appears perfect. Near the end of the school year, a French transfer student named You Tomoe joins Tsukiko's class, claiming to know her from the past. By professing his love for her, You creates friction between himself and Tsukiko's two childhood friends, who both harbor strong feelings toward her. Now that another boy is entering Tsukiko's life, Kanata and Suzuya realize that concealing these thoughts may no longer be an option.