GVG-511 Big Sister's Real Sex Education Natsuo Nana

Riona and Shun's siblings were abandoned when their mother died when they were young and their father left them with a large amount of debt. One day, the uncle who used to take care of them comes to find their house and visit them. However, the uncle's purpose is Riona's body, and he puts her to sleep and attacks him. And Shun gets an erection when he sees it. To her bewildered younger brother, her older sister decides to teach her the correct sex.