Essentials

Mackenzie Lewis isn't normal. In fact, she's far from it.
Mackenzie is one of three Essentials, supernatural beings chosen by God for a specific duty. They can't die, and any injury disappears in seconds.
And they are very /very/ important. They keep the balance between Light and Dark, good and evil. If one were to fall or join the Dark, the balance would tilt in favor of the Dark until the next Essential was born.
Darkness fears them for this, and sends their fiercest warriors, Deadlies, to kill the Importants.
And for the last 18 years of her life, being hunted is all Mackenzie had known.
Until she was Found.