Her son is about to start working and will soon be leaving home. Yui is happy that her son, whom she raised alone, has grown up to be such a fine man, but at the same time she feels lonely. Her son, whom she has raised with such care, is about to go out of reach... On their last night together, Yui is unable to contain her emotions and sneaks into her son's futon. Her son feels the same way. The two cross an unforgivable line and indulge in a forbidden love affair. However, her son's sex is far more intense than Yui expected, and he has an incredible stamina. No matter how many times he cums, his continuous thrusts never end, and Yui soon falls into a world of madness...