#Inktober Day 28 - Gift / Scarf
The term 'familiar' applies less to a type of spirit entity, and more to a function that certain spirits undertake.
To be considered a familiar, a spirit needs the strength to manifest in the physical world, they also need to have mastered the knack of catalyzing the mystic potential in an awakened mortal. Familiars have a variety of forms when they manifest in the physical realm, but the most common are animals, "intelligent" weapons or amulets, or small humanoid homonculi. In the spirit world, the true form of a familiar is revealed. Such forms often reflect the physical form, but with some differences... animal spirits might combine traits of various beasts, swords may have wings, homonculi may be full human size.
Arrogant mystics who don't regularly show appreciation or give gifts to their familiars sometimes find that their magical potential is weakened by a poor relationship. Those mystics who do cultivate a strong relationship with their familiar often find their magical potential magnified, and may gain other benefits based on the spirit's nature.