a paladin who seeks to battle true darkness by slaying demons and unholy beasts.
a slayer has studied the dark arts to better fight it, however the darkness now grows inside them corrupting them.
a slayer is a master stoic and through intense dedication and focus they keep their darkness under control, using it.
the hide and bones of demons used as armor absorbs dark magic and is highly resistant to fire.
epic slayers take demon souls into them, instead of being posessed by the demon the slayer's will remains dominant and the demon soul is forced to the bidding of the slayer.
no slayer can contain a demon forever, their soul and mind are corrupted over time.
as the slayer becomes greater at killing demonic powers they become a demon themselves, eventually in the heat of battle the darkness they have contained for so long bursts forth and they will lose control of themselves and revel in the slaughter around them.
in the code of the slayer when one drifts to far into darkness they must commit suicide, then as their corrupted soul is pulled down to darker depths they battle on for all eternity in damnation.