Hikari Yoshizawa: Jurnalul sexual al socrului meu - partea 1

One day, he stumbles upon a DVD that contains a video of his wife and a man having sex. He's puzzled, but he can't stop watching the video. Why is he having sex with my wife...? The man, who has been diagnosed with stage 4 liver cancer, comes up with an idea to continue filming his son's sex with his wife until he left. He crawls into the house at night, records the footage, and fucks his wife...