I was seduced by my girlfriend's sister Ranka and the ending Yuki was having a good time with his girlfriend, but every time they had sex, his lover wouldn't let him play naked and had to use a condom. Then one day, he met his girlfriend's sister named Ranka and something magical happened. A sassy girl, couldn't care less about condoms or that he was her sister's boyfriend, took the initiative and the two had an affair during the days he was there. I wonder what will happen.