Complex sentence: They exist outside of normal mage society, and are often obsessed with hunting and killing other mages, usually driven by a desire for repentance or a belief that doing so will cause their life to be returned to normal.
Split into simpler sentences: They exist outside of normal mage society and are often obsessed with hunting and killing other mages. This usually is driven by a desire for repentance or a belief that by doing so, their life will be returned to normal.