Unable to sleep at night, Ganta Nakami is cranky in class and unpopular with his classmates. He discovers that the school observatory, once used by the now-defunct astronomy club, may be the perfect place for a nap--but he's not alone. Fellow insomniac Isaki Magari is willing to share the observatory with Nakami, and a friendship between the two begins as they bond over the most unlikely things.

After Nakami's valiant effort in the school festival's race, Magari resumes her late-night radio streams. She opens up about living with a congenital heart defect since birth and shares her fears about her condition. Nakami pledges to fulfill Magari's dream of traveling when they grow up and, in the meantime, to support her in her current goals, starting with fixing up the observatory. Both friends anxiously await the results of Magari's blood tests at the hospital, contemplating their uncertain future together.