Tsuyoshi has a pretty girlfriend and one day he gets invited to the house to meet the girlfriend’s older sister.
The older sister (Sayama Ai), is very open-minded and she has a thing for nudity. But what he didn’t suspect is that she is a sex maniac that will put all her effort into having sex with him in the house, while the girlfriend is around.
The catch is that the older sister, unlike the girlfriend, doesn’t like to use condoms and she likes to do it raw. So the boyfriend doesn’t think twice about it.