Arisa and Sayaka are mommy friends whose children attend kindergarten in Tokyo. One day, Arisa has a fight with her husband and asks Sayaka for help. Sayaka brings up the idea of a "mistress contract." Arisa is taken aback by the unexpected story, but she accepts it without thinking. From that day on, her hidden masochistic side overflows and she begs to be trained as a masochist. She forgets that she is a mother and becomes addicted to the pleasures of being a woman. The two get caught up in a dark, somewhat fleeting, yet pleasurable lesbian sex.