Airi is living a happy married life with her husband, whom she has been dating since high school. Her husband is a kind man who does not mind going out to dinner with her best friend Mika and her husband once a month. They promised not to keep secrets from each other. However, Airi betrays both her husband and her best friend, and becomes deeply involved with Mika's husband, Junichi. When Junichi comes to visit her at home when her husband goes to work, Airi shows off her lewd side with a female face that is like that of a different person. Although she swears that this will be the last time, their secret meetings continue...