@Lauder Could I make a suggestion, but just a suggestion?
Why not have your character beginning to enjoy the blessings of Papa Nurgle? Things like a deadening of his nerves, corrosion of his armour, attracting smaller (but ever growing) swarms of flies to him?
I think that would leave room for progression through the RP - as he becomes more of a walking maggot-farm - but you can do as you like.
Of course, if he's from the Death Guard then he's likely to already be a full-blown Plague Marine, but folks need to remember that not all Chaos 'cult' groups are from the First Legions AKA Not all Night Lords are Raptors, not all Emperor's Children are Noise Marines etc.
Just thought I'd toss that out there for you to mull over.
@Ollumhammersong Well...yea, they are pretty great. I mean who doesn't love herding those slaves and cultists into the guns of ones enemies?!