Fumino is the fiance of Yuu, the eldest son of a sake brewery that has been in business for 150 years. To marry into a distinguished family, she needs the approval of her strict father... Fumino, with her pure and angelic smile, is the ideal bride... but... In fact, she has another face as the legendary prostitute "Karen-chan," who has been ranked number one for three consecutive years. Her true identity must never be revealed. She appeals to her sense of chastity and teases him by not having sex until marriage... However, for many years, the strongest Karen-chan (Fumino) unconsciously activates her "amazing technique." Yuu begins to suspect Fumino. And her father also asks a detective to look into Fumino's background... What will happen? ?