The protagonist of the tale is Niwa Makoto, a high school student who resides with his aunt and her family due to his parents' absence on business. While living there, he encounters his enigmatic cousin Touwa Erio, who is the same age as him. Erio dresses unconventionally by adorning a futon mattress around her upper torso and claims to be an extraterrestrial. Her preferred culinary choice is pizza. Erio had vanished for six months before being discovered adrift in the ocean. She cannot recollect any occurrences from that time, but she maintains the belief it was the result of an alien intervention and roams around her vicinity swathed in the futon.
