Fumino is the fiance of Yu, the eldest son of a sake brewery that has been in business for 150 years. To marry into a distinguished and distinguished family, she needs the approval of her strict father... Fumino, with her pure and angelic smile, is the ideal bride... or so she should be... But in fact, she has another face as "Karen-chan," the legendary prostitute who has been ranked number one for three consecutive years. Her true identity must never be revealed. She appeals to her chastity and teases him by abstaining from sex until marriage... But for many years, the strongest Karen-chan (Fumino) has been unaware The "amazing technique" is activated. Yuu starts to suspect Fumino. And her father also hires a detective to investigate Fumino's background... What will happen?