Notes from author
After playing through the game and seeing the dark age ending, I got to thinking: what if the character was always intent on becoming the dark lord? Only desiring power, dominance and the world as they saw fit. After becoming undead, the dark lord was turned on by the ones he trusted most in life, banished to the undead asylum. This left him broken, but in the time before his eventual escape, this despair turned his souls black and made him bitter towards all that is human, becoming hell bent on extinguishing the first flame and becoming the lord of the dark age.
Darkwraith would be a better covenant but the chaos storm is a useful pyromancy and I don't think it works without the chaos servant covenant.
Not tested yet but plan to in my next playthrough.