Rei, a mother, lives happily with her daughter and son-in-law. However, one day, her underwear goes missing, and she witnesses her son-in-law Takeshi masturbating to it. It seems that the cause is a lack of sex between the couple... Rei feels sorry for Takeshi's huge dick that is never used, and in her lust, she seduces him, saying, "I'll help you in place of my daughter." Even though he knows that she is his wife's mother, Takeshi can't contain his excitement at her lewd behavior and exposes his rock-hard huge dick to her...