This post follows on from this post I did a few weeks ago. Since that post, there's been one change worthy of noting here: the agreed-upon title is "Archduke", not "Duke"; the former is for the head of the house, while the latter is for the heads of the vassal families immediately under him as well as that of the heir apparent.
There's a thread running through this setting from the ancient past to the far future: the consequences of Genesis 6. The angels that went AWOL on God because the local women were too hot to resist never repented of their errors. Instead, they lied about it, doubled-down, and projected their failings on to others. In the time immediately before the Coming of the Azure Flames, these angels returned to the world and renewed the very activities that got them imprisoned in the first place. It is due to their actions that an otherwise flawless plan by the other notable bunch of fallen angels to do their Pinky & The Brain impression failed so dramatically and unleashed the worst of the Nephilim--the demon Legion--upon the world (in the form of a zombie apocalypse). (Lew's not happy about that.)
During these times, some peoples took the promises of false gods and other saviors and escaped certain death in exchange for loyal service; many of these were also of that same bunch of fallen angels, playing those roles, aiming to establish herds of their own to play with as they wish. The more far-sighted and capable of them took their herds off-world, establishing Conveniently Human Aliens for Mankind to encounter once Earth got sorted and going to the stars once more became a viable course of action.
What does this do?
- A single point of origin for Evil.
- A single point of origin for "non-humans": they're corrupted Men. (Hybrids, if you will.)
- A believable explanation for other setting elements: a lack of AI (too easily possessed, as they are soulless egos), why undeath is a bad thing (it's not really you, but a specific demon running your body like a corpse-puppet; think like you're playing one in a game), Full-Conversion Cyborgs require the blessing of the Church (too close to death), a taboo on the use of Weapons of Mass Destruction (part practical and part dogma; irradiated land can't be settled, and "Steward of Creation" dogma applied on the stellar scale)
- A Big Bad you can punch in the face, good and hard, like Superman can do to Darkseid. Even if you can't truly destroy them, you can beat the crap out of them and put them down for a long time. (And I haven't decided if true death is beyond a protagonist to do or not, yet; this is just for necessary reader morale purposes.) If Tolkien can do this with Morgoth and Sauron, I can do this sort of thing too.
The fundamental thread here is that of violating taboos in the name of some seaming good because the consequences cannot be seen, or if seen then accepted. Fear, pride, envy- all common elements in tales where these guys have a presence, even when not literally present. Same as it ever was, but concrete in forms that the Fall From Eden is not to a lot of people. From here, we can branch off into other themes and motifs.