A young woman named Kazue runs over a naked girl on a mountain road. When she stops to help, the girl runs off into an old abandoned house in the middle of the woods.

On her 18th birthday, Ami Nonomura wants to meet her father and brother who live far away. While searching for her brother's house, she is attacked by a thief, but is helped by Hiroshi Tazaki. They fall in love but discover that they are siblings.