Rio, a former sex worker, has never been able to hold down a man or a job for long. Currently unemployed, her only pleasure is getting on the train in sexy clothes and inviting gropers. One day, Rio seduces Sayama when their eyes meet on the train. Driven wild by his exquisite technique and experiencing ecstasy, Rio chases after Sayama when he gets off the train. Sayama is a professor of sexual medicine at a university. Sayama takes an interest in Rio and decides to hire her as his assistant, but...