Seigetsu Academy, which was once an all-boys school, is now a co-ed institution that focuses on astronomy education. Tsukiko Yahisa becomes the academy's first and only female student in this area. Kanata Nanami and Suzuya Touzuki, two of her childhood closest friends, are at her side, shielding her from the approaches of the student body. Tsukiko meets 13 different males that are based on the Western zodiac star signs as she learns to navigate her new environment. Tsukiko's contact with these lads eventually leads her down a series of star-crossed paths that would tie her in countless relationships.