My sister came to Tokyo for work with her boyfriend, who is also her colleague. Due to the surge in inbound tourism, they couldn't find a hotel in the city center, so they ended up staying at my place... My sister, who was supposed to be sleeping next to me, moved over to her boyfriend in the living room. What?! They're actually having sex in my room?! I pretended to be asleep, but it went on for so long!! Seriously, when is it going to end?! The next day, I gave my sister a stern warning! She told me her boyfriend is a "stamina beast." She apologized and begged to stay one more night, promising they wouldn't have sex again. My sister left for work first, leaving the boyfriend in the bathroom. To my shock, this stamina beast was jerking off in someone else's house! I yelled at him!! He apologized while kneeling naked, but his cock was still rock hard, which naturally led to us fucking!! That night, my sister came home early from an after-party with her staff, already exhausted. When her boyfriend returned with souvenirs, things got heated between us again...