Actually, that depend on the character you wish to play.
For those who wish to play for greed, the character would need a reason, even a selfish one, to enter these other realms to acquire what they don't have. They also need a plan to use that power, sad as it would seem, that would ultimately bring that realm under their complete control. Otherwise, why emphasize the Greed aspect of it? Next, they would have to come from a very specific realm of my creation. The reason is that stuff I said I was rambling on about. Short version; all the realms duke it out in this one special realm, and a single realm wins this battle, just so happening to be the most greedy realm of all. I just have to hammer out some simple details of it, and that realm will be complete.
As for those who play as "good people," they would only be from our own realm. These, yes, would be the people attempting to close the rips and tears. There are many other realms attempting this, however, I've already decided on a path this story is taking, so I don't want realm other that my own creation affecting it. Not because I'm conscientious since it's my story, but because I don't want to have to plan for anything other than player unpredictability, and not realm unpredictability.
There is a bit more to it, but I'm terrible at explaining things, and I'm having my friend read my explanation each time I finish one....... So far I'm at attempt 7..... -_- God, I suck. Either way, I hope that answers your question,
@Zebra