Shikigami (式神) are a kind of spirit summoned to serve a practitioner of onmyōdō, much like a western familiar. Shikigami cannot be seen by most people, but according to the Heian period onmyōji who were said to control them, shikigami often looked something like a child-sized oni demon. Although invisible, shikigami supposedly could, at the onmyōji's command, take a variety of human or animal forms, possess or bewitch people, and even cause bodily harm or death.
The famous onmyōji Abe no Seimei was believed to be particularly skilled at manipulating shikigami, and even had them performing odd jobs around the house. The Twelve Heavenly Generals were said to be among the shikigami that he employed.