Fury demons! Awesome, sneaky buggers. A very high upper level demon.
Willow’s father is half Fury making her quarter. They have demonic powers that are very strong, and is often exceeding most races of demons in resourcefulness. They also emit very cool violet fire.
But that is not all, they have an overall leader, a king. They are able to move around in the mortal human world with ease. They disguise their demonic traits and nature by using a very special rare custom built talisman. These things are genetically linked and come from family blood lines.
Fury’s are notorious for cross breeding, across races like Elementals or humans. The humans, well they are non-magical mules that can be used by a later generation to produce functional Fury demons. But when crossed with a magical race, they tend to prefer to make the demonic streak of the DNA more silent and so use the talismans to supress and hide this in the offspring. Generally these magical cross overs are experiments or flings. But the results can be quite amusing, well from the Fury perspective at least.