"Do you know this story?" Ayano starts telling a story. The scene is high school and characters named Ayano and Yuichi appear.... Naoya and Ayano trace back their high school life through her story. In the summer of the second grade, Naoya lost two important things. One is Yuichi, his close friend. He fell down from the top of the school building and lost his life... Also, Ayano, whom Naoya loved, fell down from the top of the school building as if following Yuichi. Five years later... Ayano can remember things only for fifteen minutes. She still doesn't know why she fell down. The story Ayano tells is about her high school life. By knowing the fact, he might be able to find the truth behind Yuichi's death and Ayano's behavior...