Shikigami (式神) is the term used for spirits summoned by an onmyoji or Japanese sorcerer. Shikigami are used to protect and serve their master, much like the Western concept of a wizard's familiar spirit.
There are many types of shikigami described in legends, the most common type being enchanted paper cutouts that can produce the illusion of another real-life object.
Shikigami are said to be invisible for most of the time, although they can be made visible by linking them to small paper dolls. They can also be shown as animals, especially birds.
Shikigami must be conjured through a complex ceremony and their power is connected to the spiritual strength of their master.
If the summoner has sufficient control and experience, his shikigami can possess animals and even people and manipulate them in this way; but if the summoner is careless, the shikigami may escape his control and gain will and consciousness of their own, and attack the onmyoji in revenge for having summoned them.
Usually, shikigami are summoned to perform tasks too risky for their masters, such as spying, stealing and tracking enemies.