The Mad Corpse Demon

Nikolai was the only human who was capable of necromancy, he ended up being driven mad and drained of his life force for it, dying at 25. Given the rank of a demon and sent to hell for crimes he committed while in a maddened state.

15 years after his death the young witch Aria brings him back to utilize his necromancy once again to defeat the monsters now overtaking their country.