Denpa Onna to Seishun Otoko

A high school boy named Niwa Makoto lives with his aunt's family while his parents are away. There, he meets his cousin Touwa Erio, a girl of the same age who claims to be an alien. Erio wears a futon wrapped around her upper body and eats pizza as her main food. She had been missing for six months and was discovered floating in the ocean, with no memory of that time. She believes an alien was responsible and now walks around the neighborhood in her futon.