I had been living with my girlfriend for about half a year, and we were living happily. One day, my sister came to Tokyo from Hakata in Kyushu. She was staying for a week, and I couldn't have fun with her during that time, but that couldn't be helped. "Hey! I'll be here for a week." Huh? What? Her boobs aren't big! "Hey, do you want to have sex with me?" I was seduced by her big breasts without a bra, which my girlfriend doesn't have, and her cute whispering dirty talk in Hakata dialect, and we had an affair.