Twenty years ago, three demon lords tried to claim the world for their own and waged war against those who stood against them. The war waged for 15 years and although the deaths were uncountable, the good had prevailed. The three demon lords showed to be such a threat, that the angels were forced to aid against the them. In the end, the demons were sealed away never to walk the world again. However, their power and influence did not leave the land, word is beginning to spread that a cult and their leader are planning to undo the seal and release the lords onto the world to reign terror once again. Leaders of different species and kingdoms gather to discuss the growing threat and soon come to realize that the cult is not something that can be ignored. They assemble their best fighters and send them on a hunt to stop the cult before it is too late.

So that's the basic idea, I do have much more planned out so don't think this is just it.