Magic is defined as utilizing mana to initiate some kind of effect. Naturally, this is a somewhat vague description, but for the purposes of defining magic it is the only valid one. After all, the vastness and complexity of the spells that have developed in the time leading up to the modern era is incredibly difficult to summarize.

All mana originates from the limitless Origin, where it is colorless, "raw" mana, magical energy in a pure form. When mana leaves the origin and becomes the mana supply of a mage, its quality and quantity are defined by blood. While there are ways to compensate for having low amounts of mana or low-quality mana(or both), traditionalist magi tend to feel that these methods are slipshod shortcuts at best. More modernist magi may be more open to those who use such tactics. When mana becomes a mage's source of power, it is "colored" by that mage's affinity. As a result, that mage becomes best suited to performing spells within their affinity, and the mana is no longer pure. This is not to say that a mage cannot use any spells that do not belong to their affinity, but it means that they are best at spells falling within it.

Affinities are passed through bloodlines, and can be nearly anything that is not made by man. Though some affinities are extremely rare, there is no such thing as an entirely unique one. At least, almost no such thing. There are two exceptions to this rule, the enigmatic Mana affinity, possessed only by Nakamura Kiyomi, and Death, possessed only by the Arakawa bloodline(and only in a usable form by Arakawa Yoshika, the only member of their family truly aware of the supernatural on a large scale). As previously stated, an affinity dictates what spells any given mage is best with, but is not exclusive. A mage can learn other spells, but it will be more difficult(Nakamura Kiyomi is an exception, as she can only use spells to direct mana to use it for defense and offense).

Spells themselves are an incantation or chant that allows for mana to be used to create some form of effect, be it a ball of fire, healing an injury, or anything else. The more powerful a spell, the longer the incantation. Rituals can be used to activate spells as well, and runes can be used to remotely activate spells without vocally casting them. Mentalcasting is a process that allows a spell to be cast mentally, at the cost of some power. Even the most skilled mentalcaster must say the name of a spell to use its full power. This is for magi, of course. While magi are the most wide-spread form of magic-user, Japan's onmyouji utilize a method like runes in order to cast spells, using ofuda, paper slips inscribed with various spells, in order to use magic.

A mage's bloodline does not only carry their magical potential and their affinity. In some cases, it can carry something even more unique then these aspects. A Magic Trait is a unique capability carried in some families with a variety of different effects. Each one is unique, and they do not occur in each generation. In some cases, a magic trait may vanish for decades before suddenly resurfacing. No magic trait can be found in multiple families unless there is some relation between those two families, and even then the chance of both bloodlines carrying the trait is rather slim.

Magic traits exist from birth, though in some cases are not capable of being active even if their existence is immediately recognizable. For example, Spiral Eye, the exceedingly rare magic trait of the Tallway family, is present from birth but inert for several years. This is quite lucky, as if it was active from birth, well, everything the baby looked upon with their left eye would be violently twisted into a spiral. Illusion Break, the magic trait of the Kuroki family, is also present from birth, and is fully active for that entire period of time.

Homunculi can also possess magic traits, though it is difficult to engineer such a thing in the body of an artificially-created human.

Finally, there is one magic trait that never once previously appeared in the family's bloodline. This is due to the unique circumstances that lead to its existence. Murder, the magic trait of Arakawa Yoshika, is less of a magic trait and more of a definition of the holder's nature. Yoshika is the absolute death of everything, the Living Engine of Mortality that can slay even that which is utterly unkillable.

Homunculi are artificial humans, created via the union of raw materials and the soul. The raw materials involved in the creation of a homunculus must equal, in some way, the sum total of the materials involved in the creation of a human body. As the soul is life, it is required for one to be placed in a homunculus in order for that homunculus to be capable of living. Improperly doing so will lead to a lifeless husk, or a homunculus with an incredibly limited lifespan. Due to their nature, homunculi are incapable of dying from old age, and instead will simply cease to age entirely at some point in their lives. This point can be determined by the creator or left entirely to chance.

The greatest appeal in the creation of a homunculus is the fact that they can be engineered to any specifications. They are a human who can have any skills or traits that the creator desires. A homunculus can have instinctive knowledge of any subject the creator "programs" into them, to the point where it comes to them as naturally as breathing.

Vampires are an unusual condition of being, a supernatural state of existence caused by the passing of blood, that results in a being that must drink the blood of others in order to survive. A vampire is created when all the blood of a victim is drained, every last drop. Naturally, the victim dies as a result. However, the supernatural properties of a vampire's blood cause a bizarre change when administered to a victim who has died in this manner, though it must be a very rapid replacement. The victim's blood is entirely replaced with the blood of a vampire, their heart resumes beating, and a fundamental change occurs in their nature. This is the birth of a new vampire. They no longer age, and cannot die from old age. The sun becomes a hazard, resulting in nausea and fainting if a vampire is exposed directly to it, in addition to dulling their natural capabilities. Those capabilities are an incredibly enhanced healing ability and a vast increase in both speed and strength. However, food now longer gives them any sustenance. Drink, too, feels empty. The only thing that satiates their thirst and their hunger is the blood of humans. The blood of inhuman beings often causes sickness and, in the case of even False Angels, death.

A vampire gains a severe weakness to holy items, losing the human ability to resist such a thing. In addition, their heart absolutely must remain pumping. If the heart is destroyed, their bodies can no longer regenerate as the flow of vampiric blood ceases. Their heads are also a weakness, as most things die from the destruction of the brain.

As it would be foolish to kill every person they drain from, and some vampires may have moral reservations against doing so, vampires need not drain a victim entirely. Instead, they can drain enough to merely leave that person lightheaded, or drain small amounts from multiple victims in order to fill themselves. As long as the blood is not "spoiled" it can feed them, and therefore it may be stored if a vampire so chooses.

A vampire deprived of blood will steadily lose their self-control as they grow closer and closer to starvation, eventually resulting in a mad, violent monster that slaughters humans and drinks their blood.

A thousand years ago, the archangel Lucifer fell. Its fall was so hard, so low, that the very act of falling tore reality. A hole was ripped in the fabric of reality, and it is in this hole that Lucifer has remained. The fall of an archangel, a thing so powerful, had an effect across the world. A fundamental change came in the nature of a relatively small number of humans. Some were visibly unchanged, others drastically so. The most changed sported some animal features, or even horns, leathery wings, and a spade tail. This was the birth of demons.

Demons do not age physically in any capacity, and may look identical to humans, or sport strange features such as horns and wings, or even insect antenna. They are stronger and faster than humans, and in general they also outpower vampires. The sport a bizarre capability for restoration, where damage to their body, as well as most changes, are reverted by the demon's "personal time" reversing, restoring their body to its "standard" state. For demons who were once human, this is the point where they became a demon. For demons who were never human, this is the point where their body ceased to age. The most powerful demons may even survive decapitation. Demons may possess a variety of abilities stemming from "touch" of Lucifer. They may also possess the capabilities for magic, as humans can. There is no inherent malignance in the nature of demons, but no small amount of the originals took to rather selfish pursuits in the wake of their transformation.

Demons possess a weakness to things that are holy in nature. This is due to the fact that Lucifer became the inverse of an Archangel during its fall, and as a result demons possess the inverse of divinity. Holy weapons can surpass the restoration of demons and slay them, though the most powerful of demons can resist this provided the injury is not immediately fatal, and even there there remain even more powerful demons beyond that. Supernatural forms of harm, too, can also provide more permanent injury to the demonic.

Demons can bare children with one another or with humans, but the child of a demon is always a demon. Their birthrates are extremely low.

The seven most powerful demons are known as the Princes of Hell. The Princes of Hell are incredibly powerful, beyond all other members of their kind. Satan with the Sin of Rage, Lucifer(not the same as the Archangel) with the Sin of Pride, Asmodeus with the Sin of Lust, Belphegor with the Sin of Sloth, Mammon with the Sin of Greed, Beelzebub with the Sin of Gluttony, and Leviathan with the Sin of Envy. While they rarely act in this capacity, they are the leaders of all demonkind. Once, the Church deployed executors in a bid to assassinate the Princes of Hell, but this act is now seen as a fool's errand.

One of the greatest facets of Mage Society, Mage Circles are part government office and part magical college. There are Twenty-Two Large Mage circles across the world, each taking a name for one of the Major Arcana. One of the most famed is the Tower, located in London. The youngest Circle is the Moon, Japan's Mage Circle. The purpose of Mage Circles is twofold: To serve as places of education and storing of knowledge, and to enforce rules of mage society. All circles are under the large organization of magi across the world, but they are given a great deal of freedom to manage themselves. As such, each tends to have some sort of variation in how they handle things.

One example of this is how they maintain the secrecy of the Supernatural. All circles contain a Ministry of Silence that works to uphold the secret nature of supernatural activity. However, some go about this in a nonlethal fashion, while others employ agents known as Silencers to destroy any witnesses. Another matter is in how they handle rogue elements of mage society. For example, London's Tower utilizes a special agency known as the Citadel Six(or more popularly the Unlucky Six) in order to eliminate such elements, above and beyond the usage of standard enforcers.

Mage Circles store a vast amount of magical knowledge and artifacts. Ancient Grimoires have been translated into various languages and distributed amongst the circles. A fragment of Merlin's walking stick is known to be stored in the Tower.

Education at a mage circle is favored among mage families, but not mandatory. The Tower is especially popular, receiving students from all over the world, but every mage circle gets its share of students.

The Catholic Church has, ever since its inception, deployed a variety of methods in combating the supernatural. While in recent times their views have mellowed to irritated toleration of the non-violent demonic and vampiric, and active partnership with some magi, they still house the famed Exorcist Corps. An organization composed of exorcists wielding weapons blessed by the Church's Last Resort, Saint Alessa, they are trained in the art of removing malevolent spirits from objects and people, and in the methods required to slay demons and vampires. The most skilled members of the Exorcist Corps, people who are so incredibly skilled at slaying enemies of the Church that the title of Exorcist is simply not enough, are known as High Executors. Even with these demonslayers, the Church has entirely given up on slaying the Seven Princes of Hell, as it was eventually regarded as a fool's errand.

The Church's views on magic have expanded in recent times, but an old ruling prevents teens and adults working for the Church from learning it. As such, they utilize a loophole that involves recruiting children as members of the Church and training them in magic. One location of this is a convent in England.

Saints are those blessed by a god(or gods) from birth. Of course, there are a myriad of different religions, and each religion holds its own form of Saints. The Shinto Saint Morikawa Ruriko, for example, is as much of a Saint as any other. They are rare in these times, however, and there remain only a handful of them left. Catholic Saints number on one hand. A Saint is granted an item, some form of object that only a Saint can wield, called a Saint's Tool. These pinnacles of divinity are only capable of being used by someone blessed in such a manner. They include the Dragon Slaughter Ascalon, the Spear of Longinus, and Saint Alessa's very body. These unchanging items(or in Alessa's case, her unchanging body) cannot be damaged by anything unable to overpower their divinity, and possess incredible strength. Someone who is not a Saint cannot hope to wield one, and may even be killed attempting to do so.

Dragons

Dragons are unique existences located, naturally, off of the planet earth. They serve a role as reality's defensive system, responding to threats by going into a murderous state where they destroy whatever is posing a threat to reality itself. Dragons are sapient, and each individual is unique. They range from reptilian creatures to even very humanlike ones.

Dragons' flesh and blood is composed of material known as ether, a magical substance that also composes stars on a subatomic level and can be used in multiple spells. Dragons are capable of breathing and moving in space, and are incredibly durable. No forms of non-supernatural harm can inflict real damage on them.

Dragons universally are capable of flight, even if they do not possess wings, and they can breath a destructive form of ether that rapidly dissolves matter it comes in contact with. They are very, very strong, though levels of strength vary based on the individual.

Historically, one notable dragon is the one slain by Saint George. Dragon Slaughter Ascalon destroyed it in a single blow, obliterating its body as well.

A number of more recent dragons(in the last five hundred years) have appeared in a more humanlike form more frequently.