Keep on the Borderlands Rework: The Order of the Golden Fleece
Elevator Pitch: The Keep is an outpost of the Order of the Golden Fleece with the intention of restoring Law and Order in a region tainted by creatures who are assumed to have somehow survived the flood.
So. Base the Time and Location somewhere in Burgundy during the time of the Order of the Golden Fleece origins. So either during the reign of Philips the Good or his son. I think I prefer the first. The order of the Golden Fleece was a kind of nostalgia trip for knights. Knights as a group were kind of the last of their kind as the paradigm shifted and pushed them out of usefulness in war. The focus on archers from England and the rise of canons made good old fashion, honorable melee a ting of the past. The Order of the Golden Fleece was a recall to the past. A final Hurrah for knights.
The running theory (of the human at least) is that the monsters are creatures from before the Flood that somehow managed to escape it with their devilish cunning. Wether or not this is true will need to be discovered in play. If we theme this with a JRPG flavor this type of question is very much a trope, but that's late game stuff we don't need to think about now.
JRPGs mostly work with preteen characters and the Troika way of making backgrounds is more or less a set of pre-generated characters. I think this should be cranked to eleven in a way that it's a bit like Lady Blackbird. Giving the ability to choose your own name/rename the character is also a pretty JRPG thing to do. As such I'd begin with just a few backgrounds and start from there. In Old School style characters/NPC's etc. picked up along the way may become new PC's which can then be turned into an "unlocked" background.