Well, first role-play, so I'm going to try this out.
Deep in the Sahara desert, there is a secret base, maintained by the UN. This base is used for many purposes, from human experiments to containing the most dangerous criminals. The interesting part? Everyone is under 18, and once you turn 18, you either join the government for the greater good or you will be executed. But why keep you here? Every single person kept at this facility, whether it was natural or experimental, have superpowers of some sort. That's what they do, the government takes kids from orphanages or take kids with odd abilities to experiment on.
You are one of those kids. You can choose what happened to you, and what you are going too do about it.
So, this is just the bones of it. Feedback is appreciated.