Riona and Shun are siblings who lost their mother at a young age and were abandoned by their father, who left them with a large amount of debt. One day, their uncle, who used to look after them, finds their house and comes to visit them. However, his goal is Riona's body, so he puts her to sleep and rapes her. Shun gets an erection after seeing this... The older sister decides to teach her confused brother about proper sex.