"Koisuru Asteroid" centers on Mira Kinohata, a high school student who, as a child, made a promise with a boy named Ao to discover a new asteroid together. Years later, Mira enrolls in Hoshizora High School, hoping to join the astronomy club to fulfill that promise. However, she discovers that the astronomy club has merged with the geology club to form the Earth Sciences Club. Despite initial disappointment, Mira decides to join the club, where she meets Ao Manaka, a girl who shares the same name as the boy from her childhood. Ao, passionate about geology, becomes Mira’s partner in exploring both the stars and the Earth.

The narrative unfolds as Mira and Ao, along with their clubmates, engage in activities that blend astronomy and geology. The club members include Suzu Yaegashi, a reserved but knowledgeable upperclassman; Mari Morino, a cheerful and energetic member with a love for rocks; and Mikage Sakurai, the club president who provides guidance and support. Together, they participate in stargazing sessions, field trips, and school festivals, fostering camaraderie and deepening their understanding of the natural world.

As the story progresses, Mira and Ao’s shared childhood promise becomes a driving force, symbolizing their bond and mutual aspirations. The series explores themes of friendship, personal growth, and the pursuit of dreams, set against the backdrop of scientific curiosity. The characters’ interactions are grounded in their shared passion for discovery, creating a narrative that balances lighthearted moments with heartfelt connections. Through their experiences in the Earth Sciences Club, Mira and Ao navigate the challenges of adolescence while striving to uncover the mysteries of the universe and the Earth beneath their feet.