Kousuke is a son who has excellent grades, unlike his parents. Momoko was proud of that. But her joy was shattered by a letter. It was the fact that he was mixed up at birth. Although she is sad, Momoko comes to terms with her confusion as she secretly sees him as a man... When Kousuke learns the truth, he is surprised but confesses his pain in thinking that his mother is of the opposite sex. Then, in the rain, the two of them passionately seek each other out while getting wet...