Shinya has been unable to have sex with his girlfriend Yui for a while and spends each day in agony. Then, on the first day of sex in a long time, he barges into her house in high spirits, unable to resist seeing her sleeping and defenseless, he immediately fucks her... To his surprise, it wasn't Yui who was sleeping, but his mother Rio, who happened to be visiting. Seeking further pleasure after having sex for the first time in a long time, Rio says, "This is our little secret..." and begins stroking his cock herself. Shinya, who discovered the charms of her super voluptuous body by chance, can't resist...