Ground Control to Psychoelectric Girl

The story follows a high school boy named Niwa Makoto. He lives with his aunt's family because his parents are away on business. There he meets his mysterious cousin of the same age, Touwa Erio, who happens to tie a futon mattress around her upper body and calls herself an alien. Her staple food is pizza. Erio had been missing for half a year and was found floating in the sea. She doesn't remember anything about what happened during that time, but she began to think it was the work of an alien and wanders the neighborhood wrapped in the futon.