Shikigami

A shikigami (spirit servant) is a spirit that can be summoned and controlled by a onmyouji, like familiar are summoned by warlocks in occidental witchcraft.
Shikigami's are invisible to the majority of people but they can assume physical human or animal form if ordered by the onmyouji.

Shikigami must be conjured during a complex ceremony and their power is connected to the spiritual force of their master. If the evoker is well introduced and has lots of experience, his Shikigami can possess animals and even people and manipulate them. But if the evoker is careless, his shikigami may get out of control in time, gaining its own will and consciousness. In this case the shikigami will raid its own master and kill him in revenge. Normally shikigami are conjured to exercise risky orders for their masters, such as spying around, stealing and enemy tracking.