So, I have been reading about the current situation/standing of esports. You know, scandals akin to football (shady dealings and whatnot), competition soon rivaling real life sports, etc. Anyways, people are starting to take it seriously, and I can see it having an even huger fanbase than any real sport, seeing how anyone can participate and possibly attain the dream of going pro. So, what if your game had such a following? The in-game currency could be worth real world money, the in-game items could be worth real world money, services in the game could be worth, once again, real money. This kind of universe can lead to some pretty interesting stories, because, as we all know, people will do some CRAZY things for money.
I would suggest having a wildly successful game (for the sake of easy story telling I will call it "The Game"), which numerous people have devoted themselves to playing religiously, in hopes of making a living off of something they think is fun. In the game people are able to work on as farmers on another players farm, work as a guard (perhaps the cities are run by players and they pay these guards with money generated by the economy of the city), climbing in the arena (maybe fights are broadcast on television in the real world, with adds of course to generate revenue. Combatants might even be sponsored if they are successful enough?), etc. Perhaps "The Game" could have a nigh impossible to complete seasonal quest, which awards the group which completes a very large cash prize to split among themselves.
So, for instance if you were to make a story about a guy who is trying to make enough money for his subscription to "The Game" and to live off of, you could write a story about a player who works as a farmer, who's boss suddenly buys the neighboring farm or another player. This would be very surprising, seeing how farm owners make an extremely large amount of money, which translates to large amounts of real world money.
Then after some exposition, or whatever, your character begins to suspect that the owner of your farm might have murdered the other farm owner. Perhaps your character can investigate his suspicions when logged out of the game?
Anyways, I will stop here to avoid an even larger wall of text. However, long story short, I would definitely make the core theme of your game about greed. That kind of theme can lead to some awesome stories.