Na'ian geography is superficially similar to Ya'Rian geography. Na'ia has mountain ranges, rivers, oceans, forests, all the usual terrain and weather patterns common to any world. Over the centuries, the raw volume of infernal power contained in Na'ia has substantially warped the landscape. Many Na'ian rivers are rivers of blood, and the fish that swim in these rivers have adapated to the increased viscosity and different nutrients available. Blood rain is not uncommon, although normal rain is much more frequent. Plant life is very similar to Ya'Rian flora, although there are many more species of predatory plant in Na'ia than in Ya'Ria. Most of the sub-sentient animal life in Na'ia is demon-tainted, making it slightly more dangerous and difficult to hunt than their Ya'Rian counterparts.
Na'ia is ruled separately by five (at present) Demon Princes. The number of Princes rises and falls as Princes wipe each other out or elevate underlings for one reason or another. Each Prince rules a vast expanse of territory, referred to as a Principality. Generally, Princes refer to each other's Principalities by the name of the current ruler of that land, making an accurate catalog of history difficult. While Demon Princes are technically answerable to the Betrayer, the mad god is far removed from their affairs. For most of time, the only law enforced by the Mad God is religious prohibition - worship of any god other than the Mad God is illegal, and the worship of Younger Gods is punished specifically and harshly. Mercy and Justice are concepts for which the demons have no use.
Most Princes care little for the responsibilities of maintaining a region, and so sub-divide their Principalities into Duchies. Duchies are ruled by Dukes in the name of the Prince, and unless something calls a Prince's attention directly, Dukes are the de facto dictators of their Duchies. Duchies change hands less frequently than Principalities; Dukes have fewer enemies, and those enemies are less powerful. Princes occasionally clean out existing Dukes when they assume their thrones, but the majority of Princes are content to let existing Dukes do the job they've always done.
Duchies are similarly broken down into Counties, ruled by Counts. Counts are much less powerful than Dukes, but a Count's position puts him in an optimal place for manipulating what the Duke sees and knows about the land. If all the Demon Princes were lost, Na'ian society would move along undaunted. If all the Counts were lost, Na'ia would grind to a halt.
Counties are broken down into Baronies, the lowest organizational level commonly found in Na'ia. Barons are barely treated as nobles among demons, and universally resent the mistreatment. Barons are selected by Counts from among the commoner population of the County, and barely given sufficient authority to manage their Baronies.
Commoners, the rank and file of the Principalities, are not significantly better off than the humans and other sentients. Commoners have only the rights given them by their Barons, and higher nobles rarely take notice when commoners are robbed or slain by their betters. Commoners are frequently bred for specific work; a commoner smith will have neither inclination nor ability to take up any other trade.
Na'ian hierarchy of nobility is not carved in stone or bound up in tradition. It persists because it is convenient for the Princes. There have been exceptions made in Na'ain history - some Princes jealously guard power and exercise direct control of their land. Such Princes are usually noted for excessive ego, and tend to treat even the most powerful of their servants exactly like they treat their cattle. More than one ego-driven Prince has fallen to the combined arms of insulted demons and slaves.
(Used here as a broad descriptor for the combined Races of Ya'Ria.)
Humanity occupies the bottom rung of the Na'ian social structure. Humans are slaves-of-slaves, expected to carry out any order from any demon even if that demon himself is a slave of another demon. Humans found to have qualities undesirable in slaves are frequently prepared as meals for Barons (commoners are not typically permitted to eat people). When economic hardship falls, humans are placed into a lottery, and the "winners" butchered for meat. On rare occasions, a sentient will be rewarded for exceptional service to the demons. Common rewards include immunity from food lotteries, choice of mates, breeding rights, or good healthy meals. More rarely, humans can be given the right to move freely about the Barony, to bring charges against commoners for wrongs, or to gain audience with their Barons. Rewards are handed out capriciously, but tend to be honored once given. There was, at one point, a human Baron; he was elevated to prove a "look, even a cow can do this job" lesson after a spectacular failure of another Baron. That human ruled his Barony with uncommon skill and grace, until he was eliminated by agents of the Solace military for treason against the entire race.
All known Ya'Rian races are represented in Na'ia. Many racial traits are common on both worlds - gargoyles are still resilient (even if some tend to look more like brimstone than granite), Elves are still skilled in magic, and so on. Social traits differ somewhat - notably, what Ya'Ria calls a "Barbarian" is more-or-less standard in Na'ia. The Djinn, and possibly other races, are native to Na'ia and only rarely seen in Ya'Ria.
While humanity has no political power, there is a well-coordinated movement dedicated to resisting the demons. There is also one city untainted by the demons, a headquarters for the Resistance and the only such city in the world. For further information, see Solace.
The economy of the Na'ian nobility revolves around souls. The mechanisms by which souls are bought, sold, and traded between nobles are not well understood, but it is well-known that souls are the only currency they value.
At the bottom of the social food chain, goods and services are typically traded on barter systems. The whims of Princes make any form of standardized currency impractical. Commoners trade in hours of labor (from themselves or their slaves), but the value of an hour varies greatly over time. Taxation in goods is rare, taxes instead being extracted in souls or percentages there of. Purpose-bred demons are capable of excellent craftsmanship in relatively short time. Slaves, when they are permitted to trade amongst each other or willing to risk being caught, trade mainly in food and recipes.
Principalities vary in the kind and quality of natural resources under their command. This imbalance creates opportunities for importing and exporting goods and services - one particular Prince is well-known among his kind for the quality of weaponsmiths he breeds and the quality of their work. Others are known for their skills in magic, or construction.