Eri is a single mother who lives with her beloved son Tatsuya. She and Keichi have been in love for a long time, but Eri still hides this from Tatsuya, fearing that it will affect his upcoming exams. Once, by accident, Tatsuya discovered that Eri and Keichi were fucking each other. Not wanting another man to steal his beloved mother, Tatsuya sneaked into Eri's room that night and invaded her! Although she loves Keichi very much, the powerful cock and the constant smashing directly into the uterus make Eri feel that she is becoming extremely strange. She gradually became lewd and lustful for sex. "Just one last time, after you get married, we can't do this kind of thing anymore"...