...And then there is the prospect of burning away those who prove too weak to withstand the fire, which ties in rather neatly with evolution. Consider how any of those possibilities might suit the background of the PC: is that an alchemist who sought obsessively to understand the mystery of the blue flames which surround the universe, or a popstar who was an obsession to others and never safe from stalkers? Or for something a mite stranger, the character might be a virtual idol designed to be irresistable for commercial purposes, an old oil painting brought to life by the passion of a sorceror, or an incubus/succubus from Hell.
One vital piece of information about the backgrounds in general is deciding how long these Nobles have been serving their Imperator. Does the game begin with the Commencement of the Familia as a new Chancel takes shape around them, or are they already completely familiar with its every nook and cranny after decades or centuries of service? If it's the former and the Imperator is only now claiming its realm, are they all unsuspecting mortals caught up in the last of the hundred nights which the creation of a Chancel requires, or have some of them been around longer than the others, perhaps secretly making preparations for the arrival of their lord and master? And even if the Chancel itself is old as hills, have the PCs lived there ever since its beginning, or are they merely the latest generation in a long line of Nobles, perhaps elevated to their position after the recent and suspicious deaths of their predecessors?
Also, there remains the little matter of genre preferences: should the game be influenced by Sword & Sorcery, Cyberpunk, Horror, Espionage, Romance, Western, Pulp, Noir, Wuxia...? When they are not out defending their Domains, are the PCs diplomats, teachers, mercenaries, spies, investigators, thieves, or just all-around party animals? What do you want to see in the game? And what don't you want to see?