The Elementals are a species unique to the surrounding life in a world much like Earth. They possess what are called Power Cubes, small cubes that store magical essence that gives them their powers.
There has always been two rules in their world: One, don't break your Cube. Protect it at all costs. And two, NEVER Power Swap.
Not much detail was ever given or spoken about regarding Power Swaps. So what really is Power Swapping? I guess you'll have to read to find out.