A sister-in-law who wants to change her plain self, and a brother-in-law who loves his sister-in-law like that. Unable to resist, he confesses his feelings to his sister-in-law who becomes a beautiful woman beyond recognition after receiving advice from his brother, but the sister-in-law refuses, saying, "We're brother and sister, so it's not okay...". The sister-in-law desperately accepts his request, saying, "In that case... just rub it... that's all..." and then accidentally inserts it into her slippery, wet pussy! Once they get a taste of sex, neither of them can stop, and they do it over and over again! The sister-in-law gradually becomes attracted to her brother...