Azuma Kenji is a married man with a wife and child. One day, he reads someone's online account of their wife sleeping with another man, and it intrigues him. What kind of sex would his wife, Marina, have with other men? He decides that wants her to sleep with another man. Just once would be fine. At first, Marina refuses Kenji's request, but she finally caves in to his enthusiasm and agrees do it JUST ONCE. She chooses to "loan herself" to Hiroto, a college student a decade her junior. Hiroto's the type of guy who triggers her maternal instinct. He has a habit of blowing his load quickly, but he's proud of the fact that he can easily rebound and go multiple rounds. At first, their agreement is only for a single time, but Kenji, Marina, and Hiroto all soon become addicted. Eventually, the explicit wife-loaning play escalates to extremes, like bareback sex and all-night "loan-outs”. As Marina and Hiroto fall deeper and deeper into the play, Kenji has to ask himself: is his wife really his anymore?
