Currently my character Sayuki on FEI believes that he has been given the task of holding back the gods of Death and Pestilence (Death being the god of Murder and Famine, Pestilence being the god of Poison and Disease) via the Death Guard, a group of varying size whom all use blades bathed in the blood of those who have died from disease. He thinks that killing with these blades offers up the souls of those killed in order to placate Death and Pestilence, preventing civilization from falling.
Not monotheistic, but it is an example of something different. Maybe...
Sounds a bit like Nurgle from the warhammer settings, though without the mutations granted to the faithful.
