Asami, a shy older sister with no knowledge of sex, was worried that her boyfriend didn't seem to be enjoying it. Her younger brother, who wanted to comfort her, decided to let her observe a penis, since she had never really looked at it before. However, they both got excited, and she gave him a handjob, a blowjob, and a cumshot. From that day on, her younger brother became her practice partner. Asami didn't think it was right for them to be brother and sister, but she did as he said for the sake of her boyfriend. Meanwhile, her younger brother, wanting to have sex with his sister, used all his hands to make Asami feel good, and finally crossed the line...