Everyone knows about The School, everyone talks about The School. It's the most prestigious, most impressive teaching complex in the country. Why? Because it teaches only the best, most competent, and most powerful of those who wield powers beyond that of regular humans. Whether they intend to do good or evil with those powers in future does not matter, the school cares only for your ability. In fact, villains are openly trained, mostly so that some simple rules can be followed, so that not too many innocents are killed, so nothing truly terrible happens even as they grasp for power. It's an exciting place, and these are exciting times, especially for the students. Why? Because the prom is coming up, and along with unnatural powers comes physical comeliness, many of the most attractive people in the area attend, and while most schools run the full gamut of physical attractiveness, here everyone it at its peak, the only deciding factor is personal taste, and so tensions run high as the dance approaches, and even though many of them are heroes, not all of them are great at being 'good' when hormones run high, surrounded by such temptations.
I intend for this to start simply enough, the character (male or female) may have fun exploring the school, or perhaps their classmates, in the week leading up to prom, but then on the day of... Their date, if they have one, gets called away, or perhaps distracted by someone else, and they find themselves dancing with someone they don't know. They are teased, and flirted with, and drawn to the side and in the dark hallways or a quiet bathroom are claimed in a passionate tryst, and then their partner vanishes. As they search for the one that had so... Excited them they realize the person had come over from the other prom. Their paramour had been a villain, and one that was, apparently, willing to service them again, help them feel that excitement, that pleasure, almost more tempting for how illicit it had become, but they wanted something too. They had plans, plans for the school, plans to make sure everyone was... Enjoying themselves.
The exact details of the plan, and gender of the main character/villain and so on can be left, somewhat, in my partner's hands. PM or post if you're interested.
As a different option, this could also be done with more of a rape/mind control bent, skipping the Prom sub plot, and making it more about the... Forcible conversion of a young hero(ine) to the villain's cause if anyone would be interested in doing it that way.