Ayumu is a student who is full of erotic thoughts, but is a gloomy and unpopular girl. One day, he sees Ranka, a dark-skinned Lan Hua who lives in the same apartment building and is rumored to be a slut, masturbating and giving a blowjob to a man on the stairs of the apartment building, and he accidentally takes a picture of it with his smartphone. However, it seems that she knew he was taking pictures, and later he is ambushed on the stairs and taken to Lan Hua's room.