My wife has returned to her parents' home to give birth. Perhaps out of concern for her, my sister-in-law Aoi suddenly visits our house and barges into the bathroom, saying she plans to stay the night before going back home. Although I initially reject her as she presses against me with her attractive, slender, big-breasted body, I end up engaging in a forbidden relationship with my pregnant wife, as it has been a while since we last had sex. However, Aoi is sexually frustrated and is not satisfied with just one shot. She throws away all morals and appearances and follows her instincts, so I respond by filling her vagina with a huge load of sperm!