Essentially parts of the lorebook. Will update as I go or get new ideas.
Home state
The Carnalite Regency is the official name of the state, though it is colloquially known as the Crimson Horde, something everyone decided to run with.
The Crimson Horde hails from the Steppe, in the North Eastern section of Aishiji. The weather here is steady, and has built up a strong people with a semi-nomadic culture, endlessly trying to out run long summers and brutal winters. The land here is covered in endless fields of yellow grass, with large scenic mountains to the South West border of the province and Mesa against the North Western one. Not much really grows here, apart from a peculiar herb, null grass. A common plant that sucks out all of the ambient mana from its surroundings, rendering it inert, and generally making it very difficult to perform the arcane arts in its presence (a royal nightmare for armies that rely on such abilities). How a magical race such as the Onis manage to cohabitate and perform magic with nullgrass around can only be described as the will of the Goddess. This plant when consumed will release all of its absorbed mana into its host, giving them the ability to cast wild, unpredictable spells (unless you are an Azurite). Given an Onis physical makeup, it will also give them a significant boost in overall performance.
There are multiple large cities that have been converted from their previous owners to what they are now by the Oni, with many nomadic settlements roaming around the country side. Sitting in North West with its back defended by the Mesas, lies the previous jewel of a previous forgotten state - the capital city of the Crimson Horde: Hoshiguma, named after the legendary Oni that could break the mountains in two.
Currently, the Crimson Horde is know by its neighbors for having boisterous, hard working people and their sheer love of the drink. The skirmishes are annoying (its the non-con sex mostly), however the Oni's never actually kill anybody, though there are a lot of perturbed villagers wondering how they are going to feed their new horned kids. The mercenaries that are sent out into the nearby states are also seen as a fantastic boon too, being a huge force multiplier.
Physiology
The first thing many notice about Oni's are just how large they are compared to other people, even the ones that would be considered Amazonian. The women on average stand at around 7 feet tall, and the futanari's at around 8 feet tall. Their musculature is far denser and more efficient compared to other species, meaning that a single Oni has the strength of a dozen men or so, and are naturally born physically gifted. This does mean unfortunately that Oni's are not the best swimmers. Onis also require an amount of alcohol to survive (naturally they over do this and have a particular penchant for sake, but they are master brewers of all things alcohol), just like water, and their tolerance to becoming inebriated is legendary as a cause of this; it should be noted to never try to out drink an Oni as that can prove quite fatal. Due to being used to such extreme levels of intoxication, A defining trait of the species is their characteristic horns and elf ears, though female Oni's horn are usually smaller in size or completely absent on occasion. They usually have two horns protruding from their forehead, though its also common to just have one in the center. Oni's are extremely long lived as well. Oni have an extreme defense against any mental/illusionary spells and most magic, partially being magical creatures themselves and from their built up tolerance to nullgrass.
There are 2 main types of Oni, that being the far more aggressive Red skinned type, commonly known as Carnelians. They are closer to the classic stereotype of being a fight loving drunkard. Then there are the Blue skinned ones, the Azurites, these ones are far more dangerous as they are more methodic and intelligent compared to their hot-headed Red sisters. While Azurites may be physically weaker than Red Oni's they have a huge advantage; that being highly skilled in magic and shamanism. All Onis have the ability to spell cast, however almost all magic that Carnelians can produce is used subconsciously to strengthen their bodies. Both types of Oni's get a large power boost if they consume any nullgrass (especially Azurite's and their magical abilities).
Of course there are rivalries between the two types, but its more of a sisterly banter. They are still under the same flag, and are extremely loyal to each other. The divide was far more obvious in the old days when there were more pure Oni's running around but not so much nowadays since their skin tones have homogenized to being a peachy sort of color. An Oni will be born with vibrant colored skin, but almost all of them will lose it as they grow older with their skin turning a more natural color, apart from the pure ones. However, an Oni's horns will still retain the color of their youth, so that is a consistent identifier. Hair color is also quite varied amongst them. The most common one is either grey or white hair for Carnelians and Black for Azurites.
Due to the blood being diluted with the Humans and other species they bred and conquered, some Oni's have begun to be born without a penis, being purely female. Some Oni females can pass off as a human woman as well (lacking the horns or pointy ears), just being a peculiar amazon that loves alcohol.