I have an idea, based in medieval (Or possibly early renaissance) times. The players are spirits, sort of minor gods, guarding their villages from other beasts of the land, as well as bandits. They ask for worship and taxation (Sometimes in food, sometimes in blood) in return for their deeds however, those of the larger cities asking for bigger taxes. The more dear a tax is, the more powerful the guardian becomes. However, as the faith i the spirits slowly waned, and the taxes became a nuisance, the villagers were less loving towards the spirits. Therefore when a group of paladins from across the sea landed, they went to villages and cities, slaughtering the spirits protecting them, claiming they could protect them just as well (for a lesser price) The peasants accepted this. They also killed the wild spirits of forests, valleys and gorges. This, in turn, allowed darker spirits to enter the lands, which was now guarded by fewer spirits. The paladins didn't care as they were powerful enough to destroy the spirits, however they are slowly becoming more powerful, and corrupting the land.
There are two evils:
The paladins (Who are essentially RPG heroes - they kill monsters (spirits) in a no nonsense fashion, and take their rewards from the peasants and lords.)
The dark spirits (Who corrupt the land and are currently held back by the paladins and a few of the reamining spirits)
Spirits have elemental powers based on the location they're in, so one from the plains would have good control over both mud and plants, while one from say, a canyon village would be quite hardy and have very good control over earth, both rocks and dirt. One guarding a large city would be quite mechanical, with medieval weaponry and stone armour. The exact skills are up to the role-player however.
Is that an okay idea?