The protagonist, Koshino Hiroki, lost his father 15 years ago. Since then, he lived alone together with his mother Koshino Kazusa. Knowing first hand how his mother worked hard to raise him by herself, he works hard as well to repay her and make her life easier.
One day, while Kazusa and Hiroki are drinking merrily, their sexual tension escalated, which resulted to Kazusa giving her son a blowjob. After the act, they mutually decided to forget about it.
Unknown to them, a man secretly filmed their affair. That man blackmailed Kazusa into sex, and then sent the videos to Hiroki.
The videos Hiroki received contained his sexual affair with his mother, as well as a film of her mother being blackmailed into sex. In the video, the man then proposed a game to Hiroki. If Hiroki can find all 9 porn DVDs of her mother, then the man would no longer bother the two of them. The man warned him not to consult anyone about it, including his mother.
With the desire to protect his mother, Hiroki decided that he will...