Yamada, a part-time worker who only thinks about butts, has his Rina Rina come to stay at his house. Rina doesn't listen to what people say and just plays games all day long. Rina exposes her beautiful butt without any protection... Yamada can't help but bury his face in Rina's butt... At first he is surprised by this sudden act, but halfway through he starts to enjoy it and starts to ask for more and more, as if he is toying with her uncle... From that day on, their secret relationship began.