When Niwa Makoto's parents moved overseas, they decided he would move to the city and stay with his aunt, Towa Meme. Makoto was told that Meme is unmarried and childless, but when he arrives, he finds a mysterious girl wrapped up in a futon...

Erio, despite her beautiful appearance, is a strange girl who believes herself to be an alien. One night, Erio asks to be taken to a distant beach, where Makoto learns about the incident that caused Erio to begin calling herself an alien.

Makoto is irritated by Erio's attempt to escape reality by making herself believe that everything was done by aliens. He wants to have her accept reality. However, Meme sits down with Makoto and tells him to just leave Erio alone.

Makoto broke his right arm while partaking in an 'adolescent' activity and has been stuck in the hosipital since. Erio doesn't come to visit Makoto, but his female classmates Ryuuko and Maekawa-san manage to swing by...

Meme grows desperate and crazed upon her 40th birthday. Erio gives her a gift, which spurs her on to celebrate Erio's birthday the next day, since they skipped it when it actually came about. Erio tells Makoto she wants to rejoin society.

Ryuuko rediscovers Erio's infamy. She is worried that Makoto might get ostracized at school because of Erio's past. Also, Maekawa-san decides to visit Makoto's place. Ryuuko, who has conflicted feelings for Makoto, begins to show signs of irritation...