A sci-fi friendship drama about a high school girl, Yuka, and an alien, Motomura. Motomura comes to Earth to complete a medicine for her friends suffering from a plague, and ends up sharing a room at Yuka's house by chance. The two grow close through their shared life together, but the completion of the medicine means their separation. Yuka does not want to part with her first best friend, but the day is getting closer and closer.