Makoto Niwa methodically counts the number of happy and bad adolescent events he has, as though grading his own life. When his parents leave for an extended period of time, he relocates to a new town to live with his aunt, relishing the change and eager for a new beginning. However, no matter how commonplace he envisioned his boyhood to be, he could never have envisaged the presence of an intriguing long-lost cousin. When he moves into his aunt's house, he encounters Erio Touwa, a cousin he never knew about. Erio, although being Makoto's age, is diametrically opposed to going to school and prefers to spend her days wrapped in a futon. She even claims to be an extraterrestrial with a distinct speaking style.