Nature & Appearance
Familiars exist within the Spirit Realm, a world parallel to Midgard, existing in tandem with the world of mortals. Every mortal soul in Midgard has a familiar counterpart in the spirit realm. They are connected with someone's soul from the moment that person is born, and they share their "master's" (not an entirely accurate term, but the one most often used) personality traits. The familiar can always hear the thoughts of their counterpart in the mortal realm, even when they are not present.
Despite their innate connection, familiar spirits are separate entities from their master. They have their own names and are capable of acting on their own accord. The familiar and their "master" are equals in their relationship, and the familiar chooses whether or not to obey and even whether it will come when summoned.
Nearly all familiars take the form of an ordinary animal, not a magical creature or anything humanoid. The type of animal usually reflects elements of their master's personality. Thus, familiars range in size and shape from the smallest beetle to the largest tiger, depending upon both location (familiars typically take the shape of an animal from their master's native region), and depending upon the character of their master.
The wisest of shamans can read an individual and know their familiar spirit well before that familiar is summoned, if it ever is. Knowing someone's familiar spirit can be useful in assessing the true nature of their character. For instance, if someone who seems trustworthy has a serpent for a familiar, it may be time to reevaluate them. However, it is also true that many familiars are terribly misjudged, and thus one should only trust a knowledgeable shaman to interpret whether someone having a rat familiar means they are intelligent and enduring, or if they are a cowardly betrayer, or possibly both.
A familiar spirit's abilities are, essentially, the same as any ordinary animal of their type, but with incredible and uncanny intelligence on the same level as their "master." However, the bond between the familiar and his or her "master" allows them to communicate in ways no other creatures can. The "master" and the familiar can communicate to each other through their souls, not unlike a form of telepathy, and they can hear each other's thoughts. The familiar cannot communicate with anyone else in this way, however, nor can they speak aloud.
In some cases, summoning a familiar spirit may not even be necessary. Sometimes, a person's familiar actually seeks them out, especially if they are strong of spirit. Many people may be accompanied by their familiar without even realizing it, in the form of a pet or animal friend, and they simply do not know how to communicate with them. They may go their whole lives accompanied by their familiar in various forms but never realize it.
In order to directly summon one's familiar, the person must be able to reach into the spirit realm using Spiritual Magic, whether through their own means or with the aid of a shaman or druid. The person need only request, in his or her mind, for their familiar to come to them. If the familiar is willing, they will appear, and the two must make an agreement regarding whether the familiar is willing to be summoned to the mortal realm. However, not all familiars come when called, particularly if they dislike the manner in which their "master" addresses them, and often it can take several visits and a considerable amount of coaxing for one's familiar to answer their call.
When a familiar spirit is killed in the mortal realm, they are cast back into the spirit realm until they recover their strength, at which point they can (if they are willing) return or be resummoned. However, when a familiar is "killed" (temporarily banished back to the spirit realm) in Midgard, their master also suffers a terrible blow to their own soul, weakening them for so long as the familiar is still recovering in the spirit world. Even individuals who do not realize that an animal is their familiar will suffer spiritual and emotional trauma when that animal is killed.
Many individuals who summon their familiar spirit enchant certain items to become anchors for their familiar. Most anything can be made into a familiar's anchor. Using the anchor, the master can summon or dismiss their familiar spirit more easily through a direct connection - though, of course, the familiar still needs to be willing to answer that call. Using anchors allows the summoner to dismiss or summon their familiar as convenient, in hopes of avoiding their familiar being "killed" in the mortal realm.