Shoko Takahashi's mother married her depraved new husband without her knowledge, Shoko was often forced to have sex with him by her stepfather, she couldn't resist because he was the only one who supported the family. Shoko's younger brother accidentally saw it all while coming home from school, and he recorded a video of his sister having sex with his father in the living room.
Then the number of times he saw it got more and more, until he was discovered by his stepfather, and at that moment, the desire to fuck his sister like his father was doing urged him to run right into the group...