The protagonist, Akifumi, enters the same school as his childhood friend, Mizuki Minato, and they enter into a romantic relationship. They are a shy boyfriend and a shy girlfriend, and although there are times when things get awkward between them, they spend three years together holding hands, peacefully and happily. However, one day, Akifumi finds out Minato's secret: that this innocent girl has been undergoing physical development for three years. A vivid record of how her entire body was turned into an erogenous zone over the course of several months... A record of how she was taught the techniques to please a man... And a record of how many times she climaxed... What Akifumi found was a record of his beloved girlfriend's body being transformed into an "adult body" by the hands of another man. Flat-chested × NTR ~A record of my childhood friend's training over three years~ [Translated from the official website]