Specifically, the character of Malachi. As a fluff background, he's got it made as descendant of the first of the Nephilim and embodiment of the gate that will allow demons into the world. Now, this is good to begin with, but the personality that he has been given by the writers shows a twisted ability to plan and build up favours.
For instance, and the major reason I'm writing this, he apologises for an outburst he made to a ghost character by offering to help her find companionship. He asks her to choose someone that she would enjoy spending time with if she could. 30 seconds later, the woman she chose is dead. When he needs a favour, and after the two ghosts are beginning to connect, he says "You do have a choice. Does she find out why she died. Or not."
I'm not selling the series or it's characters at all well, but the series and it's premise could easily be transposed into the Heptagram by a cunning GM.