Takasora Hoshi’s home life is abruptly crowded when her schoolmate Umi Mizuike and Umi’s mother temporarily move into her family’s small apartment. Takasora and Umi initially agree to stay out of each other’s way, but irritation gives way to curiosity as Takasora notices how much of Umi’s life remains unknown to her, including the places she disappears to at night. Forced into close everyday proximity, the two high school girls begin seeing sides of each other that school never revealed and confronting feelings neither expected from the arrangement.