I had an idea similar to the one mentioned above. I called it crystal quest for the irony of it.It was basically what truly else said, a deconstruction of rpg archtypes from a different point of view and whatnot.
You're this mercenary guy that's usually just playing around and stuff, but a mercenary none the less. Not the leader of the party, but not the runt of the pack. Just another mercenary.
One day, the group is approached with a job to smuggle a certain item to a neighboring country. You accept, not knowing that the item was one of the crystals that were stolen by some evil or whatever a while ago. check out one of the final fantasies for details or whatever.
So, one of the kings/emperors/democracies sends the 4 heroes after your jolly band of mercenaries, and they kill everyone. Brutally, just so they could recover the crystal. You fall of the cliff and escape, but everyone that you know, even the noob that had joined two days ago, was killed. On one side, the heroes were supposed to recover the crystal at all costs, and the mercenaries were just evildoers anyways, right? On the other, everyone you have known for years is now dead.
So here you are, the last surviving member of your group, half dead and enraged at the ones that were hailed as the heroes and saviors of the world... Your own journey begins, to kill the heroes to avenge the deaths of everyone, and from this mission you set out to topple anyone in your way.