Yamada, a part-time worker who only thinks about butts, has his niece Maika come to stay at his house. Maika doesn't listen to what people say and just plays games all day long. Maika exposes her beautiful butt without any protection... Yamada can't help but bury his face in Maika'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... From that day on, their secret relationship began.