Mizuki shows her firm student council president attitude even to the sexually harassing teacher, Tanabe. Though she feels lewd about her beloved younger sister, Aika’s uncharacteristic remarks, she sees her off as she goes off to extracurricular volunteer activities… Mizuki is called by Tanabe, who shows her an obscene video of her younger sister, and in exchange for her promise to dispose of the video, she accepts the man’s demands. Her consciousness gradually melts away as she experiences something new for her, and she trembles with pleasure…!?