Reiko raised Sarina, her only daughter, alone after her husband died when Sarina was young. That daughter also grew up and got a boyfriend. Sarina's boyfriend was a very friendly young man, the second son of a sake shop. Reiko was very happy that the young man was Sarina's boyfriend. But... the young man had another side... That's right... he was incredibly skilled in bed... and had a strong dick. One day, Reiko was shown the young man's erect dick. Reiko, desperately trying to maintain her reason, said, "How can I be attracted to my daughter's boyfriend..." But... instinct destroys her reason... What decision did Reiko, who could no longer stand it, make...?