Maina, a high school girl, is sexually trained by her common-law stepfather, who she has always found disgusting and has always had a physical aversion to. In order to avoid upsetting her mother, she initially resists the many perverted acts he forces upon her, but she eventually accepts them. However, her young body adapts quickly and she falls victim to the extremely nasty training. One day, her stepfather uses Maina's plump body to start a new job...