Familiar

Familiars (使い魔) are special assistants used by the magi. Since it's natural for a magus to separate himself from society, the use of familiars capable of performing small, simple errands is considered orthodox. Although a different entity, familiars are seen as an extension of the magus as there is both a mental and physical connection between the two. The symbol of the magus itself and fundamentally different from creatures like the Demons or Spirits who are summoned and then bound by a contract.

Nature
There are several ways to create a familiar. The most traditional is by placing the leftover thoughts of an already departed soul, of a dead person, into the body of a dead animal. Following that, the magus needs to repair the animal corpse so that it can move again and by transferring a part of the magus body, that has a great concentration of Magic Circuits (eyes, hair, blood, etc.), into the body of the dead creature in order to give it a new life. The resulting familiar will gain Magic Circuits that the original never had before and will be able to use Magecraft just like the magus. However, prana cannot be produced independently and must be supplied by the magus through their spiritual connection. Thus, a familiar requires a master to maintain both his powers and life.

This type of familiar will form its own personality and will be capable of reasoning and acquiring experience apart from the magus while sharing the same knowledge. Mages need something that has about the same level of rationale and reasoning, but can think independently. That way they can act as a teacher, and have the familiar be a teacher to them, too. It is better to discover new things that way, and it also makes it easier for them to realize their own mistakes. There is also a chance of the arising of abnormal powers. A good example of this would be Len, who not only has succubus-like aspects but is also capable of living for long periods of time without a master and forging contracts with individuals other than her creator. However, the presence of a personality also makes this type of familiar more independent from the magus and many magi really do not like that method. But some mages make insurance by passing everything on to their familiars. To explain it simply, it is a spare self that is a little behind on abilities. Important to note that this is by no means a form of resurrection, as the familiar is still a being completely different from the one whose soul it received.

Additional notes
Familiars like the ones mentioned above can be made out of pretty much any creature: cats, dogs, birds, etc. Actual, living animals can be turned into familiars as well and magi prefer this type more as other types since they are quick created and easily controlled by them. But these animals become magical monsters over time and the best example for this are the Blood Worms who make up the body of Zouken Matou. Humans can also be turned into familiars, but that is seen as a monstrous act and impractical (due to the prana burden) by most magi. Also, familiars without souls can be used, however the modern versions of these are weak.

Completely different types of familiars also exist. Examples of those include Cornelius Alba's slimes, magic constructs such as Touko Aozaki's puppets, and spiritual beings such as human ghosts and nature spirits. Note that, strictly speaking, a Servant is not a familiar and rather falls more towards the side of summoned being. Servants are called familiars only due to some similarities (spiritual connection, dependence on prana) and for the sake of formalities. They need to be put on a class of their own however, as it would be impossible to summon Heroic Spirits without the help of the Great Grail and there is no need to use something as powerful as Command Spells to control regular familiars.

Transfer of the master's consciousness into the body of regular familiars is possible and most magi do so to remote control them while they are in recon or exploring missions. However, it is impossible to perform transfer of consciousness with a familiar that has its own soul and personality. In this case, the best that the magus can hope for is the sharing of senses with the familiar (like receiving a video-feed of everything that the familiar sees and hears).

While it is possible to transfer one's consciousness/soul into a creature with an existing soul, this is nearly impossible. Even transference into a familiar without a soul doesn't mean that the magus has completely transferred himself. Destruction of the body (this also includes through natural means like aging) of the magus will mean the destruction of the soul of the magus. But there are ways to get around this, for instance, complete transference of the soul using the Dress of Heaven, Roas resurrection, or the vampiric method that Zouken Matou had resorted to. Nrvnqsr's 666 beasts (or rather body itself) are also familiars. What makes these particularly different from other familiars are that they all are generally equal in power as each one of them is Nrvnqsr himself.

List of Familiars

 * Black Hound - Cornelius Alba
 * Dragon Tooth Warriors - Caster
 * Slime - Cornelius Alba

Ghost Liner
ゴーストライナー

The greatest type of familiars. Servants are close to this type.

Owls
梟 - Fukurou

Small statues of amethyst in form of owls that Rin Tohsaka uses for reconnaissance purposes.

Projection Machine
幻燈機械 - Gentou kikai

Created by Touko Aozaki to replace the familiar that was destroyed by her sister. A suitcase with a projector installed inside. It shapes Ether Clump in the form of a monstrous cat that cannot be destroyed unless the suitcase is destroyed. It also has the ability to heal Tohko by enveloping her.

Puppets
人形 - Ningyou

A special type of familiar that are not any kind of life form, but rather mystic constructs whose actions are controlled (directly or indirectly) by the magus. Their users are known as Puppet Masters (人形遣い) and follow the philosophy that the magus himself does not need to be strong, but rather he needs to make the strongest creation. Known Puppet Masters are Touko Aozaki, Cornelius Alba, Van Fem and the unnamed Master of Assassin during the Third Holy Grail War.

Aoko Puppet
青子人形

A puppet that Touko Aozaki crafted to resemble her little sister, with a crow mode and a spider mode. It can self-destruct.

Automata
自動人形 - Jidou ningyou

Automated puppets shaped after humans that the magus can control as if they were an extension of his limbs. Puppet Masters that use these usually are not suited for direct combat. Examples include the French dolls-type that the Master of Assassin mentioned above used, which were equipped with deadly weapons for precision killing.

Demon Castles
魔城

Giant golems created by Van-Fem, there were seven of them at first, but #5 was destroyed by Fina-blood Svelten.

Sealed Box
封印の匣 - Fuuin no hako

Another of Touko Aozaki familiars, a black monster with a thousand mouths and thorn-like tentacles stuck inside a box. It drags its victims to inside the box so it can eat them.

Shadow Giants
影の巨人 - Kage no kyojin

Sakura Matou’s familiars made out of her Shadow element. Under normal circumstances they are extremely small but, when her powers are augmented by Angra Mainyu and the Holy Grail, their sizes increases vastly and start acting as a materialized curse. Each of them is composed of roughly 1000 units of prana.

The Dead
死者 - Shisha

The deceased. The familiars of the Dead Apostles who deceive death by sucking the blood of other people. Created when the corpse of the one who had his blood sucked and then received some of the vampire's own blood does not manage to become a Ghoul. Several ranks stronger than the Living Dead, but still mindless and soulless puppets that are to 100% controlled by their creator. They completely consume the flesh of their victims in order to maintain their bodies but over half of the absorbed energy is sent to their master.

Worms
淫虫 - Inchuu

The lowest of all familiars. Used by Zouken Matou. Loves feasting on the energy of humans. When the host is a male, they consume their bone marrow and part of the brain after shattering his spine, making him crippled in the process. When it is a female, they absorb the mental energy created after sexual stimulation is made through the nervous system. Usually don't consume the flesh of women, but the uterus is their favorite meals. Will eat the placenta after giving its victim sexual pleasure strong enough to fry the nerves of the brain. Shinji Matou's Book of False Attendent is made out of these.