The mortal realm and the netherworld are separated by the Veil, also called the Aether, which the gods Sealed after their war with the demigods and demons. Though, no one's actually seen a god since the Veil was closed. Some speculate (or blaspheme, depending on who you ask,) that the gods are dead. Others think the gods simply washed their hands of the mortal realm after having to slaughter their own demigod children for getting uppity. But most people think the gods alive and well and watching over them, for good or ill.
Very few aetherial (i.e. supernatural) beings, the so-called immortals, have the ability or strength to breach the Veil. Demons and fae can be summoned into the mortal realm by someone who knows their true name, but only for a limited amount of time. Still they're only in their spirit form, which is pretty strong in its own right. Their actual bodies remain in the netherworld. Some lesser demons and fae were in the mortal realm when the Veil was Sealed, though, and their descendants live among humans. Some peacefully, some not so much.
Only sentinels, the winged servants of the gods are allowed to pass through the Veil's barrier at will. Though once in the mortal realm, they' re invisible to (most) eyes, unless they chose to reveal themselves (usually in their human form, because their divine form can be rather terrifying, or at least overwhelming.) Each sentinel was molded by his or her patron god and quickened to life with a drop of said-same god's divine blood. The gods, and only the gods, possess the power to breath life into inanimate objects. Even the demigods have to produce life the old fashioned way, by procreating. (Though some immortals do have the power to trap the spirit of others into inanimate objects or move spirits between bodies, but it's considered taboo, or at least very rude.)
It's generally believed that all magic originated in the netherworld, also called the otherworld or realm of the gods, and it includes the realm of the fae, the realm of the dead, and all twelve hells. But it's of great debate as to whether magic was a gift from the gods. Or a the result of interbreeding with the gods (or fae, or demons, or some combination thereof.) Or simply innate abilities humans already possessed.
Regardless of its origin, human magic is divided into three categories: sorcery, magery, and witchery. There are all manner of other preternatural talents as well, generally referred to as gifts, or curses, such as clairvoyance, divination, psychometry, etc. But telling the truly gifted apart from fraudulent swindlers often proves difficult.
All magic is hereditary, but some types are more dominant than others, and it can often skip generations. Women are slightly more likely to manifest powers, making up sixty percent of "Magic Weavers," or Weavers for short. But despite the seeming prevalence of magic, Weavers make up only ten percent of the human population. Still, they far outnumber immortals, who make up less than one percent of the entire population.
Sorcery is the most powerful kind of magic, and also the least common. At most, sorcerous families only produce one child per generation who actually manifests powers. Sorcerers and sorceresses have a great deal of raw magical power, or spiritual energy, within them. Though their reserves can be expanded over time with practice and training, they only have a finite amount. And once its depleted, it takes time to recover and replenish their reserves, like with blood loss.
If a sorcerer uses all of his or her energy at once, they'll die. A sorcerer with the knowledge and training can transfuse energy between sorcerers, but the two types of energy have to be compatible, to oscillate on the frequency, as it were. If the two energies are not compatible, the backlash, like concussion waves after an explosion, could potentially injure or kill anyone standing too close.
Despite their raw power, sorcerers are limited in scope, however, because each sorcerer has only one kind of innate ability. There are hundreds of different types of sorcery, and it can take years of training and research to discover his or her specialization. But even two sorcerers with the same specialization are not alike. They each Weave their personal style to the magic, and not all sorcerers are as strong as one another.
In order to boost their reserves, all sorcerers have familiars, using magical creatures as a reservoir to store excess raw power. A sorcerer's familiar is formidable by itself, generally relying on brute magical strength rather than cunning. It bonds with one sorcerer, and when the sorcerer dies, the familiar dies with him or her.
The opposite is not true, however, and a sorcerer might have more than one familiar in their lifetime. Sorcerers usually bond with their first familiar when they're only eight-to-ten years old. The bond is not always consensual, however. It's not unheard of, and in some families it's even a rite of passage, for young sorcerers to capture and subdue a familiar using only the power of their will.
Demons are the ultimate familiars. Lesser demons are highly coveted, but it takes an extremely strong sorcerer to bond with one. Greater demons are more likely to have sorcerers for familiars than the other way around. And no one, not even the gods, have subdued a Royal Demon.
Regardless of the familiar's species, it can only be understood by Weavers, other familiars, some bestial immortals, and demons.(Greater demons' magic is fundamentally similar to sorcery, minus the limits of specialization, and they also use innately powerful familiars.) There are Translation spells that allow everyone else to understand the growls, meows, or chirps, etc. that familiars make when speaking. Few people bother, though, as familiars are rarely far from their masters' sides. (Familiars, on the other hand, understand everyone else just fine, despite humans' unnecessary tendency to speak loudly at them.)
Unlike internally powered sorcerers, mages get their magical power externally, drawing their power directly from the environment around them. Specifically, they draw on one of the elements (as defined in magery): air, fire, water, earth, metal, wood, and aether. Each mage has an affinity for only one of the elements, and it's usually quickly evident which one. Though, in some rare cases, a mage can control two elements. No mage in recorded history has ever been able to control more than two elements.
In order to direct their power, mages require the use of a focus, such as the proverbial staff or rod, but any number of objects will do. Jewelry, such as rings, bracelets, necklaces, and pendants are common foci. Though few mages actually use the a staff as a focus, they all carry one as both a symbol of their status, and a weapon in case magic fails. Whatever form their focus takes, it's of their own creation, crafted by their hands, shaped by their will, and empowered by their Weaving. Crafting their first working focus is the final test required of young mages in order to graduate from Apprentice to Fellow.
Because a mage's focus is so instrumental to their Weaving, they often craft multiple foci over the years, each designed with a unique purpose. It can take years to accomplish the first one, but after that it tends to take only weeks, months at the most, to craft those that follow. And to protect them from potential thieves and enemies, those foci are hidden among mundane jewelry, bangles, and other accoutrement. Each focus has it's own individual limit of stored energy, and needs to be recharged periodically. It can only be recharged a few times before becoming unstable, though. In which case the mage has to safely dismantle it or risk it frying like an overloaded circuit.
Although mages are much more common than sorcerers, their magic almost always skips at least one generation. Even when two mages have children, it's unlikely any of those offspring will manifest any powers. However, their grandchildren have a fifty percent chance of being mages too. And if the grandchildren are mundane, the great-grandchildren are ninety percent likely to have powers.
Because they can't pass their knowledge down from mage parent to mundane child, mages tend to pool their knowledge together. They congregate in local guilds, religiously guarding their dusty tomes, studying the laws of magic, and debating magical philosophy. They each record their own spells and acquired knowledge in a personal grimoire, which is posthumously added to the guild's library. They rely on conjuring and evocations, using obscure or even nonsensical words. The words themselves are not important, they are simply a way for the mage to give shape to his or her will.
Of all the Weavers, witches are the most likely to "breed true," and as such, are the most common by far. If both parents are witches, their children are ninety-eight percent likely to have powers. And even with just one witch parent, the chancess are eighty-five percent.
Witchery harnesses the power of nature through various combinations of incantations, potions, brews, and charms. Their spells are all pre-made and can take a great deal of time, depending on the intricacy of the spell. They can store some magical energy within themselves for later use, but they can't generate it internally, like sorcerers do. And using all that energy at once won't kill them, because it's a considerably smaller amount compared to a sorcerer.
Like mages, witches record their spells, building on the lessons passed down through his or her family. But instead of grimoires, witches use familiars as a repository for their knowledge. Unlike socererous familiars, a witch's familiar doesn't have any magical strength of its own, just a remarkable memory and a lack of aging. And it only bonds with whom it choses. Once a familiar bonds with a witch, it usually attaches itself to his or her family, and can be passed down through the generations. In addition to being fiercely loyal, witch familiar are also highly intelligent, as is necessary for a walking, talking, and usually furry, library.
Everyone develops at different speeds, but in general, sorcerers tend to start manifesting power when they're only five or six, whereas mages and witches manifest during their mid-to-late-teens. Most preternatural humans, such as Seers, etc., have their "gifts" since birth, but some don't manifest until puberty, in their tweens and early teens at the latest. The abilities among the immortals varies wildly. But as a general rule, demigods and other extremely powerful beings don't manifest their abilities until adulthood, and they stop aging once those abilities do manifest. Usually the younger an immortal looks, the more powerful she or he is.
Weavers age slower than most human, living around three times longer than mundane mortals. The oldest Weaver on record was a witch who lived to be three hundred twelve years old. To her credit, she didn't look a day over ninety seven in human years.
All mortal magic, and immortal abilities for that matter, require balance in order to work: the energy output must equal the energy input. If the attempted output is greater than the input, there's an energy backlash could be fatal. Mortal magic, in particular, also requires a catalyst. Specifically, a sacrifice. In the case of sorcery, because sorcer-ers generate their magical power internally, they sacrfice their own energy. But because mages and witches draw their power from external sources, they must catalyze their spells with their own blood. In the vast majority of cases, a single drop of their blood suffices. The more blood used, though, the greater the sacrifice and more powerful the spell.
Using other people's blood in spells, though, is a whole other story. Blood magic can be seriously powerful, and in most places, it's strictly prohibited. Each city-state has different ways of dealing with magic, though. In Blackmire, as long as only mundane animal blood is used, it is technically legal, but it's still generally frowned upon. In most places, though, it is legal to sacrifice animals as offerings to the gods, as long as it's done in the temple by a certified priest. Not that that stops many people in Blackmire from performing their own sacrifices at their home shrines, especially in the lower, poorer levels.
Only one human in a hundred thousand is born a Void. And of those, few are allowed to survive to adulthood. Immortals, in general, consider Voids a threat, an aberation, an abomination to be destroyed. Because Voids have no spiritual energy of their own, they must feed on the energy of others in order to survive, absorbing it through their skin like the way some amphibians absorb oxygen. Voids can drain all the power from immortals, Weavers, and the gifted, simply by touching them. Rendering them simple mortals, if the Void stops in time. And killing them if they don't.
Despite their rarity, Voids are not generally hard to find. The gifted, Weavers, and immortals can immediately sense it when in the presence of one. Just like they can usually sense power in others from the energy radiating from them like tiny suns, they can also sense the black hole where a Void stands, pulling energy from the very air. Even mundane humans and animals can sense Voids, to some extent, like a general feeling of unease.
Although Weavers fear Voids and immortals hunt them, there are those who believe Voids are the gods', or perhaps nature's, way of providing balance to the world. The priests belonging to the temple of Kuroshu, a goddess of justice, in particular believe this. The priests and priestesses of Kuroshu scour the planet for Voids, hoping to gather them into the protection of the temples ahead of any immortal's blade.