My sister came to Tokyo and decided to stay at my apartment for a while. I lent her a shirt to change into, but it turned out to be her boyfriend's shirt! She was relaxing in that outfit, and I watched her defenseless and sexy appearance for days, and I got a boner! My sister found out and it was awkward... but instead of getting angry, she suggested a round of sex, saying, "It's okay as long as you don't put it in," and I gradually got soaked! "We can't have sex because we're brother and sister... We promised to only do round of sex," she said, but I inserted it raw and came inside her wet pussy!