Nagi Umino learns that he was mixed up with another child in the hospital and was not raised by his parents. He decided that he would not change anything in life: he was old enough to calmly survive this news. On his way to meet his biological parents, he meets a girl, Erika Amano, who tells him about that her parents want to marry her by arrangement. Therefore, she invites him to play the role of her boyfriend in order to avoid marriage. Arriving at the meeting, Nagi Umino discovers that it is with this girl that he needs to marry – since it was they who were switched.