You were an experiment, you've always been. UA went on a trip to an underground lab where you were in. A scientist led them through the building and introduced them to some of the experiments in their cages then they came to your cage. You were in a room behind a black door that was highly secured

Scientist: And that's 001's cage. He's the youngest experiment yet he's been here the longest.

(State your OC when you enter the story)