The eldest son of a sake brewery that has been in business for 150 years, Yuu's fiancée is Fumi. To marry into such an esteemed family, she needs to be approved by her strict father... Fumi, with her pure and angelic smile, should be the ideal bride... or so it seems. In reality, she has another face as the legendary #1 hostess 'Karen-chan' for three consecutive years. Her true identity must never be exposed. She emphasizes her chastity and teases by refusing sex until marriage... However, the strongest Karen-chan (Fumi) unknowingly activates her 'amazing technique.' Yuu starts to suspect Fumi. Meanwhile, her father hires a detective to investigate Fumi's background... What will happen??
