Six months into a happy life with my girlfriend, her cheerful adult older sister comes from Hakata to stay for a week. I expect nothing worse than temporarily losing our privacy, until I see the sister's enormous braless breasts. Then she whispers cute Hakata-dialect filth in my ear and asks, “Want to fuck me?” Overwhelmed by the double temptation my girlfriend cannot offer, I give in, cheat with her sister, and cannot resist filling her with cum even while my girlfriend is nearby.