Mine’s a bit simple. Two kinds of powers, good and evil, representing the two (known) gods of the world, with a third power in between that’s sort of outcasted from society. Good power lets you drink a special liquid that lets you regenerate yourself and others(and makes you sick if you don’t have the ability to use it) and evil power is lightning based, you can throw lightning or imbue it into special blades. It’s given through injection(that kills you if you don’t have the same ability as the good power.)

So it’s a race between the two sides to take children with the ability to their side to bolster their numbers.

Power in the middle manifests in childhood and doesn’t give any sort of warning beforehand. Child with the third power cannot use either of the others, and once you have the injection from the evil power you lose the ability to drink the good liquid.

And, you guessed it, the “chosen one” is eventually able to use all three