Yume and I have been living together for a while. Because my girlfriend had a training session, I had to stay alone for two days. While resting, someone knocked on the door, and it turned out to be Ai, my girlfriend's sister. She came back from the US to Japan for three days. Due to my girlfriend's mistaken date, she was about to leave. But all hotels were fully booked, so I kept her to stay. Indeed, Ai has a very attractive figure. Especially her big breasts that I couldn't take my eyes off! After she finished showering, I don't know if it was accidental or intentional, but she didn't wear underwear! Her pussy was clearly exposed in front of me! Ai also noticed my gaze, approached me, and actively let me touch her pussy and squeeze her breasts! Unable to resist her allure, for the past two days, I have ejaculated more than my entire life combined! The feeling of guilt and pleasure makes me unable to stop.