Yusei, a son whose father remarried and doesn't think well of Mako, who has become a new mother. - One day, Yusei forcibly rapes Mako and films her with his smartphone, and uses that as a material to threaten Mako and train her to become a tit-fucking sex slave. - Yusei's training escalates, and while her father is away, she restrains Mako with a DQN senior and makes her cum with an electric massager and vibrator, and then fucks Mako's big boobs with a senior with a big dick. - Mako gradually went crazy as well.