After Takahashi's mother died, Naoto and his father lived alone for a while, then his father remarried, and Takahashi got a new, pretty mother, and a lush little sister. As it should be a big boy, his hormones are in full swing, and Naoto fantasizes about his stepmother and sister, but in reality he is very shy. And, one day he notices that he accidentally installed on his phone application which suggests getting to know any girl better, for fun he performs simple manipulations according to the application, and suddenly he realizes that he had moved into the body of his sister. Insidious thoughts crept into the boy's head, now he can know all the delights of the girl's body, through his own experience. He is now more likely to make his first acquaintance with the girl's body than he bargained for, and will he ever have the perversion or misfortune of making an application for it? We shall see...