Ryuu turned one of his own fictional universes into a mafia. That sounds like an idea for me to steal, as I have a fictional universe as well, I just haven't done anything with it yet. The plan is for that universe to be turned into an RPG some day (so I have characters and stuff), but the chances of that happening aren't very big, so I could always just go and base a mafia around it.
That is, once I'll be playing mafia games again. Which is not yet.