Book where teenager discovers he has fire powers. A boy a little older than him has lightning powers. They train together and become best friends. They fight someone with metal powers. They discover that they are in a simulation and there are other teens with different elemental powers. The boy with the fire powers likes a girl with water powers. There is a boy with a nuclear energy power. They live in an underground facility. The rest of humanity lives in that facility. They were given powers to fight the aliens that invaded earth.(the aliens have elemental powers). There was one boy who had mental abilities.