Nagi Umino was mistakenly switched at birth, and now attends a prestigious private high school. One day, he has a chance meeting with Erika Amano, an incredibly high society highschool girl who claims she's on the way to meet her fiancé, and who asks/forces him to be her fake boyfriend. Neither of them, at the time, understood the significance of their meeting for Erika was the girl Nagi was switched at birth with…