Heart Blade by Juliana Spink Mills

The Heart Blade will rise in light, or in darkness.

Teenage half-demon Del Raven wears a promise in scarred letters upon her skin. Now, pressured to make her first kill and seal her demon nature forever, she flees her pack and forges a dangerous partnership with young angel-blood Ash.

But Del isn't the only one on the run from the demons. For seventeen years the Guild of Saint Peter has done its best to hide orphan Rose, a key player in the centuries-old Heart Blade prophecy.

The threads tangle, and soon Del, Ash and Rose find themselves in the crosshairs of an ancient war between demons and angels... and the hunt for a mythical weapon that could change the balance of power forever.