History is written by the victors, as the mortals say.
The Aesir and the Jötunn. The Seelie and the Unseelie. The Gods and the Titans. The Fall of Lucifer. Ripples of shadows of the truth, passed down in half-guessed whispers to mortal ears and told and retold, until nothing remains but the fruits of human imagination, and the memory of Schism.
Spirits are everywhere, behind and between the world seen by mortal eyes. They enact the will of their beating heart, the God-Machine. They build metaphysical infrastructure, channel incomprehensible power, protect, people; whatever the God-Machine decrees. Sometimes humans sense them, and call them guardian angels. If only they knew.
You are no angel.
You are one of the Unchained, the unholy, the unclean. When the Schism ended, your kind had retreated into the depths of reality. The God-Machine cannot bring down the Underworld without laying waste to all reality. The Underworld cannot strike at the God-Machine without bringing their own destruction. Humanity has become their battleground, the field where the Cold War in Heaven is played out.
You walk amongst humans, in a world of false identities and conspiracies, stolen faces and invisible technologies. Each day, you defy the God-Machine in the service of your kin, living in fear of discovery. But your kin are ever distant, and trust in your handlers frays in the face of treacherous conspiracies. Sometimes the only ones who understand are the angels on your tail: for the sake of Heaven, you are all in Hell.
Basically Demon the Descent, but with a shift in power dynamic. Instead of one central authority with apparently perfect knowledge of all its agents versus a bunch of scattered renegades, there are two major metaphysical blocs: the “Seelie” and the “Unseelie”. This is meant to address the fact that out-of-the-box Demon is far more like an insurrectionist movement led by outcast ex-politicians than a Cold War.
What they once were does not matter - it may not even be clear to the Spirits themselves. What is known is the fact of life, which is to say, the Schism. However many they once were, now there are two. Two great factions that are irrevocably opposed, and seek total mastery of the multiverse.
The Seelie are the victors of the ancient Schism; essentially unified, given the freedom to shape humanity over the millennia, interpreted as various flavours of angelic beings in their interactions with mortals. They are ruled by the God-Machine, which you don’t know very much about other than you (or possibly your ancestors?) rejected it in the Schism. Since you’re all vaguely Matrix-y entities, it’s possibly a type of governance or a hive-mind or an ideological meme or something. They greatly favour technological advancement amongst humans, possibly with the aim that humans will eventually become enough like them to be incorporated.
The Unseelie are currently the underdogs, on Earth at least, though there is little difference in actual power between the two factions. They lurk in a different part of reality that’s hard for the God-Machine to influence, with limited interaction with the material world, but are still extremely powerful. They have a broadly feudal system of governance, with nested layers of principalities. There may well be other reaches of reality, other mortal populations, who are under the sway of the Unseelie rather than the Seelie. But the playground for this game is humanity, who are well within the influence of the God-machine.
Any further direct clash between the two blocs would probably destroy reality, or at least wipe out most of the spirits and render everything a blasted wasteland. Instead, they seek to build power over humanity, since this influence helps to determine the relative strength of each bloc. The Seelie have significantly more influence at present, and thus as Unseelie agents you are in constant danger.
All that being said, there is more going on than meets the eye. Factions juggle constantly for power within the blocs, individuals have their own egos and agendas, and politics is a matter of constant deception. You can’t rely on your handlers, and they can’t rely on their employers, and they most certainly can’t trust their overlords. Your kin dwell comfortably in the distant reaches of existence, utterly incapable of understanding you. And much as you might despise the angels working to turn humans to their own advantage, and hoping for a chance to kill you – at least they know what it’s like.
Gameplay would be basically like Descent, but the assumption is that the God-Machine is not overwhelmingly powerful on Earth and that angels are its servants rather than actual parts of it. You need to fear its attention, but it is still limited. The God-Machine doesn’t automatically know the identity of angels and demons, so disguise and infiltration and double-agents are entirely possible.
Angels aren’t just mindless drones until they’re on the verge of falling; they’re individuals with their own agendas and views, different levels of allegiance to the God-Machine, different attitudes to humanity and to the demons. It is entirely possible for spirits to pass from either bloc to the other, not just in the one direction from Angel to Fallen.
And there are unaligned spirits who just hang around on Earth doing their own thing, not firmly bound to either power bloc, and often able to muster enough power amongst themselves to reign in the excesses of the Angels and the Demons. They dwell in and harvest the metaphysical power produced by the physical realm, just as both Angels and Demons exploit it for themselves, though most of it is appropriated by the God-Machine.
You can still have the classic “small factions and local power blocs and making your own connections” bit, because Those People Back Home just don’t understand what’s it’s really like here on neutral (if somewhat compromised) ground. You don’t necessarily have any specific orders when you’re sent here, and you certainly don’t begin with a neat set of contacts. Spirits tend to form loose networks, which include human agents (typically bound by pacts), unaligned spirits and potentially even contacts from the other side.
Thoughts? This is only a first attempt at the concept.