Ririko's husband had to go on a business trip alone, so she moved in with her daughter and her husband. Although it is better to live alone, Ririko has always felt lonely and deprived of sex. Every night she had to masturbate herself to comfort her body. She also spotted the shadow of a giant cock peeking out the door, which seemed to be masturbating with her as well. She also guessed that the person was probably her son-in-law. Discovering that her daughter did not like to have sex with her husband because her husband's cock was too big, her son-in-law always had to deal with it alone. Ririko immediately came up with a bold thought, which was to sneak into the couple's bedroom and soothe her son-in-law's huge cock! "It's all because of Keiko and Kunio-san", "Blowing a trumpet doesn't count as adultery, does it?". Awakened, but Kunio couldn't control Ririko's overly attractive body, and the two kept having sex even though Keiko was sleeping next to him. Their bodies seem to be born for each other, and they constantly make love and orgasm over and over again whenever Keiko is away. The two can't seem to live without having sex with each other...