The Night All Angels Cry
Everything should be normal-none of you can remember anything that indicated the Time of Judgement was imminent, no sudden unbalancing of the scales between Heaven and Hell. So why has everything changed? Why has the Final Battle occurred? Why can you not remember it, despite being on the battlefield when you woke up? And at least as important, where has the majority of the leadership for both sides gone?
Hopefully some of these questions will be answered by the end of the game, even if just so I know the answers. The PCs will be angels, demons or other members of the heavenly and demonic forces, shortly after the Final Battle.
The system is likely to be Nine Worlds (http://www.indiepressrevolution.com/xcart/product.php?productid=16249), although this might change if people can suggest a better system for the game (in my opinion).