Kyû ni hen ni natchauno yo...?(1987)

In a neat little izakaya, office ladies Mayumi and Chikako, student Etsuko, and housekeeper Kazuko are in the middle of a secret conversation. The four are a close-knit group of friends since high school, and today they are sharing their sexual experiences. Etsuko achieves orgasm by combining masturbation and actual sex. Mayumi, who was raped by a coworker, has become distrustful of men and now specializes in masturbation. Chikako is obsessed with extramarital sex. Amidst all this, the innocent Kazuko is constantly aroused and excited. Eventually, Kazuko returns home and uses a kokeshi doll to masturbate for the first time and gradually experiences a true orgasm.