Foxes are small, to medium sized, omnivorous mammals that belong to the Canidae family. They are around the size of a small jackal, or wolf, in terms of reality. There are different kinds of Foxes in reality, depending on the terrain or climate mostly.
In mythology, Foxes are given the trait of being cunning, or a trickster. Especially Japanses Mythology, where they are known as Kitsune and are said to be tricksters, and even be extremely smart. Of course, the more tails they have, the older and wiser they are, equaling up to 9 tails at most. Pretty basic, in terms of the contract, these Foxes are capable of using some elements and what not. Its an old contract, so most stuff are pretty vague.