[Quick Summary] [Setting] [Tone] [Rules/Setting Conventions]
Nobilis has much in common with In Nomine, an RPG based upon the War between Heaven and Hell. In Nomine angels and demons tend to be a bit more "down-to-Earth" (literally) than Nobilis PCs. However, if you want to run an In Nomine campaign that is mythic in scope, Nobilis would be a good choice. This page explores that possibility.
Note: I will not spend much time explaining either In Nomine or Nobilis; the assumption here is that you are at least somewhat familiar with both. If you're not, some of the terminology will no doubt confuse you. But here is a very brief summary of each, just to orient someone who has no idea what either game is about:
In In Nomine, player characters are (usually) either angels or demons, who are collectively known as celestials. Celestials come from either Heaven or Hell, naturally, and can corporealize on Earth in physical bodies called "vessels." Killing a celestial's body sends him back to his native plane in Trauma, but it's very difficult to permanently destroy a celestial. Even the weakest celestial is quite powerful compared to a mortal, but it's a "superhuman" scale rather than a "godlike" scale; an angel or demon vs. a human will usually not be much of a fight, but there areexceptional humans who could be a match for a low-level celestial, at least in some arenas.
Most celestials (including PCs by default) are ordinary Servitors of an Archangel or Demon Prince. Archangels and Demon Princes (collectively known as Superiors) are the most powerful beings in the universe, next to Lucifer and, of course, God. For game purposes, they're usually treated as more or less omnipotent. A celestial who serves very faithfully and well will eventually earn Distinctions (ranks, such as Vassal or Baron) from his Superior, and may someday earn a Word. To become Word-bound is the pinnacle of achievement for a celestial (other than becoming a Superior, of course). A Word-bound celestial will be known as "The Angel/Demon of Photocopiers" (or whatever).
Aside from celestials, the only major third parties in In Nomine are the ethereal spirits who dwell in the Marches (the realm of dreams), the most powerful of which are the old pagan gods. There are also undead, Soldiers of Hell and Soldiers of God, Saints (reincarnated human souls who have returned from Heaven to aid humanity), sorcerers, and rumored Children of the Grigori.
In Nobilis, player characters are called Nobles or Powers. Most Nobles are former humans who were chosen for whatever reason to become servants of an Imperator. Every Noble has an Estate, which is very much like a Word. Nobles are vastly powerful; in some cases, a PC can permanently change the laws of reality, even retroactively (i.e., making it so that reality has always been what the Noble just changed it to...)
Nobilis is much more epic than the usual In Nomine campaign. It's a diceless system in which combat is more likely to be a battle of wits (who can use their Estate in the cleverest manner) than sheer firepower. Mortals are, for the most part, spear-carriers. The Nobilis setting is complex, confusing, and not easy to get handle on. There are several different factions of warring Imperators, of which Heaven and Hell are just two. All of the factions have a mutual enemy in the Execrucians. On Earth, there is also a sort of deux ex machina known as Lord Entropy, who is presumed to be the most powerful Imperator in Earth's plane of existence, and who sets rules that all Nobles and Imperators must follow.
For more, check out either game, as well as my own In Nomine page.
The assumption I make here is that you are using Nobilis rules to run an In Nomine campaign. Using In Nomine rules in the Nobilis setting wouldn't make much sense. Importing the In Nomine setting into the Nobilis setting is a possibility, though there are a number of differences between In Nomine's Heaven and Hell and Nobilis'. For one thing, in Nobilis, every true angel and demon is an Imperator, and only a handful ever leave their own planes.
An In Nomine Nobilis campaign will treat every player character as a Word-bound angel or demon. Depending on how mythic you want to the campaign to be, you might say that every celestial has a Word; there are no "ordinary" Servitors -- at least, none that come to Earth. The nameless Cherubim and Seraphim of the Heavenly Host, and the equally nameless hordes of Hell, stay in Heaven or Hell, waiting for the final battle, and only the most powerful angels and demons are released to venture to the corporeal plane. Alternatively, perhaps there are un-Worded celestials on Earth, in which case you are closer to running a "normal" In Nomine campaign, but at a higher level, since the PCs represent the Word-bound.
Using Nobilis to represent celestials means putting them on a vastly higher plane than humans. No angel or demon is a trifling being; while some are definitely more powerful than others, they're all godlike as far as humans are concerned. The gap between mortals and celestials, already large in In Nomine, becomes a vast chasm in Nobilis. In Nomine allows an almost "four-color comics" style of game, in which angels and demons behave much like superheroes and supervillains. This doesn't work well in Nobilis, where Nobles can generate miracles as needed. No mortal can pose much of an obstacle for a Power, and Nobles usually don't go at each other physically; two Nobles throwing destructive miracles at one another is a lot like a nuclear exchange between superpowers.
This doesn't mean that humans can't be interesting characters in Nobilis, or that plots can't revolve around them. But it will take a bit of GM finesse to put a human in a position where he can act as a foil for a Noble. One possibility is to make In Nomine Nobilis a game about individual souls, in which angels and demons are sent to save (or damn) specific people who have been identified as important for whatever reason. Thus, vastly powerful beings capable of altering reality must covertly influence the destiny of Ken Jacobs, high school janitor, without revealing themselves as agents of a higher power.
Another possibility is to forget about individual humans, and make Powers responsible for securing major battlegrounds. Perhaps India and Pakistan are about to go to war, and Hell (for inscrutable reasons) wants the confrontation to be forestalled, while Heaven wants India to inflict serious damage to Pakistan without getting the United State involved. Or Heaven wants to see the space program tank, while Hell wants very badly for man to reach Mars by 2010. The Player Characters will be responsible for using their Estates (Words) to accomplish their side's goals.
Most In Nomine rules can be handled within Nobilis' framework with a little flexibility. I will not be providing detailed mechanical conversions. For example, In Nomine Essence = Nobilis Miracle Points, more or less; just use Nobilis rules for acquiring and using Miracle Points. Most Attunements can be treated as Gifts, as can Songs. (See Characters, below, for more on characters.)
One of the most important concepts that needs to be translated into Nobilis is Disturbance, since this is the game-balancing aspect that prevents celestials from running amok in In Nomine. Without Nobilis' Lord Entropy, it's even more necessary when all the PCs are Word-bound demigods who, with no restraints on their actions, could easily reshape the world.
Most things that cause a Disturbance in In Nomine cause an equivalent amount of disturbance in Nobilis In Nomine. However, using gifts and performing miracles only creates a disturbance when Miracle Points are actually spent. This will have the effect of allowing celestials with high Attribute ratings in certain areas to perform powerful feats without disturbing the Symphony. (An angel with level 5 Domain, for example, can wield his Word/Estate to create miracles of up to level 5, without creating a disturbance directly -- though killing a human should still cause the normal amount of disturbance.)
Perceiving disturbances will have to be left up to the GM, as with most things in a diceless game, but Aspect would be the appropriate Attribute for sensing Disturbances.
It's strongly recommended that you give Judgment and the Game real bite in In Nomine Nobilis. When celestials disturb the Symphony too badly, don't just slap them on the wrist. Have triads of Judgment or demons of the Game (Word-bound, of course) descend on the violators and haul them before Dominic or Asmodeus. The descriptions in Nobilis of the punishments Lord Entropy inflicts at his Locust Court are pretty good ideas for what Asmodeus might do to a careless demon. As for Dominic -- depending on how bright your setting is, he may be extremely harsh, or he may be downright cruel, but for certain the PCs won't like the consequences.
Another alternative is to use a variation of the option rules suggested in the In Nomine Game Master's Guide; inflict damage on celestials who deserve the Symphony. This could come in the form of wounds or lost Miracle Points.