Hina's mother and Kenta's father had just remarried, so the two became sisters. Hina is an extremely intelligent girl on the surface but very shy, she was chosen to be the representative to read the speech at the university graduation ceremony. Kenta is just as shy as Hina, but he's not as smart as his stepsister. Therefore, her parents ask Hina to help Kenta pass the upcoming college exam. But Hina has a secret that others don't know, and that is that she is very fond of sex! Every day, Hina "accidentally" rubs her tits against Kenta's body, exposing her panties to expose her pussy in front of him. Even when Kenta saw the scene of sex with her boyfriend, Hina deliberately let him see it more clearly. Unable to resist the charm of the stepsister, the two secretly fucked each other right in front of their parents! Of course, their parents didn't find out because Hina covered it with her long skirt. But even so, the two still have to try to limit the noise, appear as normal as possible. The feeling of excitement when it can be detected at any time makes Hina feel extremely hot. She even made Kenta fuck naked and cum in her pussy! And since then, in front of her parents, Hina showed that she was the one who cared about her younger brother, trying to help him study. But in reality, the two are secretly fucking each other non-stop...