When I returned to my parents' house for the first time in five years, my grown-up sister greeted me in a miniskirt and knee-high socks, showing off her defenseless buttocks. She showed me her naked body in the bath, showed me her masturbation, and showed me sex with her boyfriend. She knew I was erect, but she said, "I really want to have sex with you, big brother." I couldn't resist the temptation of my sisters, so while the family was away, I'd give them a lot of sex education with my dick.