The province of Kami was devastated by the civil war, long before the fire fell from the sky or the waters rose to wash away the fields. The famine and plagues that came after killed nearly every person who had once lived in Kami. It is wilderness, now, populated by tribes of primitive men who once knew how to build cities of stone and wood. Oni rule this place - led by fiendishly intelligent Tiger Oni, and worse things. They raid in all directions, killing and plundering, and fleeing back to Kami when their raids are done. Many bands of Giants are also said to dwell here, in the mountains and hills of Kami.
East and North of Kami was once known as the Imperial Reserve. It was a huge swath of land, untouched by men, where game roved and monsters lurked. The Golden Emperors used to hunt their with a thousand followers. Now the land is silent, but for the creatures and animals that dwell there - now called the Gohan Wasteland.
Kami society is very hierarchical, with a clearly defined caste system. The ruling class is made exclusively of Tiger Oni. They are both the most naturally intelligent and charismatic of the various oni breeds (or so they would have you believe). Rulership is not passed down family lines, but rather there is something of a meritocracy among the Tiger Oni for their various positions. Often this is determined through a battle of wits, magic or claws.
The military is largely run by the second caste, the Ogre Oni (or so-called Ogre-Magi). These towering creatures are excellent tacticians and are naturally skilled in the art of combat. Though legions are officially commanded by a Tiger Oni, the Ogre Oni function as the de facto commanders in the field. On the field, they are often seen astride dire lions and elite companies of lion cavalry are often used to mop up battles.
The third caste in Kami society is the priest caste. The Serpent Oni are the sole denizens of this caste. Their connections with the eastern "gods" (who are more often demon princes, devil lords or powerful guardinals than true gods) is instilled upon them from birth. Since many of these "gods" prize treachery, deception and darkness, the priest caste is often used militarily as spies.
The Avian, or Tengu, Oni fill the fourth caste which is the lowest true caste of oni. They are primarily used as scholars and scouts. They seem to have a natural proclivity for the study of ancient, arcane and foreign texts so this role suits them very well. Tengu Oni who are assigned as scouts are closely connected to the Ogre Oni, being used as messengers and forward scouts for the military. Small companies of them are sometimes used to infiltrate and strike strategic military points.
The vast majority of Kami's population fills the fifth caste, known as the "mortal caste". It comprises of all the non-oni who live within Kami's borders. Primarily human, this caste also contains elves, Half-Elves, goblins, hobgolbins, tengu, dwarves and Flen. The bulk of the labor in the country is conducted by this caste, which is separated into sub-castes based on how close their interaction is with true oni. As what the true oni need changes from season to season, these sub-castes are often in flux, but high merchants and temple acolytes are often at the top.
Since all true Oni can shapeshift into humanoid forms, cross-breeding is not uncommon. These "half-breeds" have formed something of a partial caste, between the oni and the humanoids. In most respects, they are treated as "mortals" but they are sometimes chosen to join in the ranks of their oni parent's caste. When this happens, they are treated as just less than a true oni of that caste. If, for example, the child of an elf and a Serpent Oni were to be taken into the temple, she would be treated as slightly inferior to the true Serpent Oni but would be treated as superior to all "mortals" and even the Tengu Oni.
The final caste, the nameless caste, belongs to the Bugbear Oni. Treated almost as caged beasts to be deployed when brutal savagery is desired, the Bugbear Oni are not allowed in the cities. They tend to wander the roads, pillaging and raping any who cross their paths. Occassionally, Tiger or Ogre Oni military commanders will coerce bands of Bugbear Oni to join the military and unleash them as wolves upon the enemy. At all other times, they are completely ignored.