Eri is a single mother living with her beloved son Tatsuya. She and Keichi have been in love for a long time, but Eri still keeps this secret from Tatsuya, afraid it will affect his upcoming exam. One day, Tatsuya accidentally discovers Eri and Keichi having sex. Not wanting another man to take away his beloved mother, that night Tatsuya sneaks into Eri's room and takes her by force! Despite loving Keichi, Tatsuya's strong manhood and forceful thrusts into her womb make Eri feel increasingly strange. She becomes more and more lascivious, craving for sex. "Just one last time, after mother gets married, we can't do this kind of thing anymore"...