It's an older hentai I just can't find. It starts with a guy in his room spying at his sister through a hole covered by the eyes of a poster. The sister gets fucked and he masturbates until he shoots cum at his ceiling. Later he goes with a girl in a love hotel just to find out that they are sharing a room with his sister and her friend. They end up having a foursome and talking about how there girls like being fucked.