Magic is different depending on where one is, and the world in which they reside. There is a sort of universal magic that applies everywhere, its rules immutable and far stronger than any magic from which it descends. However, as elemental as that magic is, little can be done with it.

Universal Magic

All magic requires power, energy. Something cannot arise from nothing.
Knowing the name of something gives power over it.
All souls contain an essential vitality, energy, which can be used in the absence of any other power to fuel spells.
The transference of vitality from one thing to another requires, in at least some part, sacrifice on the part of the transferer.

A form of magic that operates entirely under the principles of universal magic is true names. Indeed, unlike all other forms of magic, the invocation of true names is just the practical application of the four rules.

Souls

The essential vitality that lives on even after death. Souls are what empower magic, the difference between a cantrip and a true spell being to what degree it uses the power of a soul. A magical act that would use less than the full breadth of a soul to cast is considered a cantrip; these actions can be performed essentially infinitely, without draining a soul of all its vitality. A spell, by contrast, will consume all the vitality of one or more souls in attempting to cast it.

When someone is alive or their soul is otherwise inhabiting a living body, their vitality will always restore to their capacity over the course of a full night's sleep. In the event that they are unable to enjoy a full night's sleep, their magic will not restore whatsoever. A character who is either projecting their soul outside of their body, or otherwise not inhabiting a living body, must find alternative means of restoring their soul

Transference

Anyone, no matter their proficiency with magic, if they have a soul they may choose to grant power to another. This power cannot be granted easily, however. For a consensual transference of power, it must be in the form of a sacrifice. These sacrifices can be as subtle as acts of worship, they need not necessarily be grand displays of power.

There is also, of course, transferences of power that are not consensual. This is often in the form of cannibalism. Eating another person requires no special magic, no technique, no practice. If someone is eating the body of another, then each morsel will imbue the cannibal with the essential power of one soul. If the cannibal eats the heart of their victim, then they have by this same token eaten their victim's soul.

Capacity

The capacity of one's soul is measured in souls. Because some souls are inherently more powerful than others. The worth of a single soul, for the purpose of magic, is thus:

A fireball, roughly 3x3x3 meters.
Lifting and moving something weighing up to 100kg for one minute.
Shoving something up to 200kg back up to five meters.
Conjuring up to 1kg of material in any shape or configuration that the caster can imagine.

The only way to raise one's capacity for power is by the consumption of other souls. For characters, this is reflected by a trait on their profile if they have consumed more than one soul. When someone's soul is consumed, the whole of their power goes into them. Meaning, if that character had two souls worth of power, the person who ate them now has three souls worth of power.

If a character eats something that is in excess of ten times the amount of power they possessed previously, that character becomes irradiated with magic, as the power is more than they are ready to sustain.

Some characters, or entities, have altered their own souls to be able to consume the souls of others in ways other than blunt cannibalism.

Final Death

When a character has had all the power of their soul consumed, when they are too weak to take power from others, they are essentially dead. Their souls may still be conjured, but they retain no memories past the point where they died, and they cannot take meaningful actions beyond what they are imbued with the power to do. The moment they are no longer being sustained by the power of something else, they are dead again and retain nothing of the time they were conjured.

Antimagic

Characters with the soulless trait cannot use magic, unless the magic relies on a source other than their own soul to conjure or direct the energies involved. This is not quite the same as antimagic, though. The simplest and most powerful form of antimagic would be knowing the true name of a given system of magic. If one learns its true name, they have power over it; that power may then be used to deflect, or it could even unravel the entire system of magic altogether.

Countering

The more common form of antimagic is countering one spell with its inverse. Life cancels out death; fire cancels out water; and so on. The only caveat is that the spells must be of equal power, and actually come into contact with one another. A clever mage can bypass a counterspell by just maneuvering around it, while a powerful mage could simply overpower it.

Ayarian Magic

The kinds of magic on the world of Ayaria are mainly descended from the Hours, or if not the Hours directly, then from Ayaria. Without Ayaria, there would be no magic on that world and it would be impossible for the Hours to have changed it so dramatically.

The laws of Ayarian magic:

The part is equivalent to the whole. One is able to target Ayarian spells with only part of their target's true name. One is able to cast a spell on a fragment of a thing, and be able to manipulate the whole thing; or, target the whole of a thing and the same spell still affect the fragments.
Bridges go both ways. When a connection is formed between two things, both sides are able to interact through this connection regardless of the intent of the one who bridged the connection.

Runic Magic

Each Hour is associated with a rune. These runes are associated with domains. When the symbol of a rune is invoked, and imbued with the power of the invoker's soul, a magical effect happens depending on what the rune in question does.

The casting of runic magic takes more power than it should. When one attempts to cast it, one soul's worth of energy always seems to disappear into the aether, not affecting the spell. Meaning that it is impossible to cast for anyone who does not already possess two souls worth of capacity.

Sigils

A sigil is a rune that has been carved, painted, or otherwise imposed onto the surface of a thing. This can be in the form of a tattoo on the body of a mage, just as well as it could be a sigil engraved on a ring, or carved on a paving stone. It doesn't matter where the sigil is or what material it is on, as long as the sigil is legible.

If the sigil is carved correctly.

The order in which Hours are evoked matters. If an Hour is invoked in the wrong sequence, or with Hours who are not compatible with them, the effect of the spell may change. Up to and including the death of the mage attempting to conjure them, in retribution for the mage's ignorance.

Gestures

Beside for sigils, gestures are the other way that runic magic is cast. One is able to make gestures with their hands that correspond with the runes in question, and in so doing produce a magical effect. Typically, the tips of fingertips or the knuckles of the hand align to form the points of a rune to be able to make the appropriate gesture.

Casting Runic Magic

Once a rune or series of runes have been produced, by gesture or by sigil, the mage must imbue the rune with power. If the caster is invoking multiple runes at once, they will produce a more complex effect. If the magic is triggered by a sigil, the effect goes off instantaneously. If the magic is triggered by gestures, then the mage must spend one round making the gestures, and then the spell will go off at the start of their next turn.

A list of all runic spells can be found here: Ayarian Runic Spells.

Domain Magic

Domains are typically associated with gods. A domain can be anything: life, death, fire, and so on. A god, or godlike being, may choose to instill the power of a domain into their follower. This will be reflected on the character's profile as a trait, and that trait will allow them to access spells associated with that domain.

If a character has begun to grow their magical potential by consuming the souls of others, they will be able to cast more powerful spells of that domain, more often.

A list of all spells by domain can be found here: Domain Spells.