When Konohata Mira was young, she joined a camp in her town and encountered a child around the same age as her, named Ao. After they promised to find a new planet and name it Ao, they parted ways. Mira enters Hoshisaki High School and plans to join the astronomy club in order to fulfill her promise with Ao but starting from that year, the astronomy club and the geography club have joined together to become the "Earth Science Club". After leaving with no choice, she heads toward the "Earth Science Club" and encounters Manaka Ao, the child whom she exchanged the promise to find the new planet. Despite being surprised by the fact that Ao is a girl, Mira also finds out that Ao has treasured their promise. Thus, the story of the Earth Science Club activities with the astronomy class's senpai Morino Mari and the geography class's senpai, Inose Mai and Sakurai Mikage, Mira, and Ao has stared.