Sei Saotome, a fifteen-year-old, is inclined to falter at pivotal moments. She had almost given up on high school but ended up enrolling in a school that surpassed her capabilities. At this institute, she encounters the audacious and admired Taiyou Udagawa and the fanciful and celestial-obsessed Mizuki Ootaka. Following Mizuki's invitation to join the Astronomy Club with the duo, Sei discovers that high school life isn't as dreadful as she had anticipated.