In a world consumed by darkness, a boy loses his father and watches his mother taken by demons. Years pass, and he grows into a relentless hunter, slaying demon after demon in search of the one that stole her away. But when a mysterious demon offers him hope of seeing his mother again, everything changes. Now, he must protect this demon from an angel determined to end it. Once a slayer of demons, he becomes the guardian of one… and the true battle begins.