Familiars

Familiars are beings that are bound to a mage via magical contract. Nearly all things can become familiars, the only requirement being that it has a sentient soul. Humans and humanoids can even become familiars. A varient parallel of this magic exists in Japanese-type worlds as Shikigami.

What are familiars?
Familiars can be a variety of beings so long as they are linked to a mage via magical contract. Some examples of familars are magic spirits (Willow, Snow), Pokemon, and even Vampires (Lolita used to be Nero's familiar)! Humans can even become familiars to other humans, with the correct rites.

What can familiars do?
Familiars are very special beings in relation to the contract with their master. Powerful mages can benefit greatly from having familiars because a familiar will share in their master's power (though it does not work both ways). So the more powerful the mage is, the more powerful the familiar will be. The contract symbolizes a trade of some individual freedoms for power.

Familiars can also grow spiritually themselves, increasing their own powers. This power transformation will go through several stages, usually marked by how well they can communicate. The most basic ability for a familiar is to communicate with their Master telepathically, while the next step up from this is to communicate telepathically to others. From there they can reach the ability to speak verbally (if they were unable to before), followed by being capable to transform into the same species as their master (usually human) physically. Though their powers aren't as effective in this form, it can help them blend into society with their masters better, baring a few traits that may give away their magical nature (such as Snow's white hair and red eyes). Transforming into their master's species marks the highest point in power a familiar may achieve without borrowing power from their master, and in addition to spiritual might requires a strong bond between master and familiar.

Familiars also inherit the Master's immortality, should they be immortal.

Where do familiars go when they aren't summoned?
A familiar's body is made out of magic and is reconstructed every time they are summoned. In this way, when the summoning is finished the body is broken back down into magic while the familiar goes into a sort of "dreaming" state within the Master's soul. A familiar will draw on the mage's magic only to construct the body and not the entire time they are summoned, and they have a certain amount of power themselves so they do not immediately draw on their Master's power to use their skills. However once they run out they are either forced to return to their dreaming state or draw on their master's magic.

If a familiar's contract is cancelled their body will be reconstructed for a final time with magic before being cut off from the Master - essentially turning the familiar back into a normal being. Though it is unknown what exactly would happen if an immortal Master cancelled a contract, it is assumed that since they exceeded their natural lifespan the released familiar would instantly be destroyed by the force of time.