When she was young, Mira Kinohata met a boy named Ao at a town camping trip. While gazing at the starry sky together, Mira discovers that there is a star with the same name as herself, but no star named Ao. The two then promise to one day explore asteroids together and find a star to name after him. Several years later, Mira enrolls at Hoshizaki High School and decides to join the astronomy club to fulfill her promise. However, she learns that the astronomy club will be merged with the geological research society to form the earth science club. Reluctantly, Mira goes to the club room and is reunited with Ao Manaka—the person she made the promise to explore asteroids with—and is shocked to learn that Ao is a girl. The two are joined by upperclassmen Mai Inose and Sakurai Mikage, second and third-year students from the geological research society, and Mari Morino, a third-year student from the astronomy club.