A Demon is an Icarus that has become a ghost. As a Ghost, Demons have the ability to choose hosts known as Demon Carriers.
It is said that demons are born from a dying Icarus who has enough willpower to lock themselves between life and death. Demons are very rare and dangerous. It is said that many demons take over convicts, as they are attracted to anger and sorrow. Many also take over dead bodies, making them into zombies. One demon, Ban'sarde (A Banshee), took over a dead girl and made her into a ghost that haunted people for centuries.
However, a renegade society of Demons, the Sin Seven, made good use of their powers, bestowing them upon Jack Pickles.