"Kami" is a Japanese word meaning, roughly, "spirit". Japanese occultists use it to refer to angels, ghosts, God and even some xenoforms, but outside Japan it has entered the occultist's lexicon as a term for very old, often very powerful ghosts who have forgotten their mortal identities. Japan has many such spirits, likely due to the prevalence of Shintoism. What often happens is that a ghost will be remembered and prayed to by its mortal descendents and so will remain on the mortal plane. It will acquire the ability to affect the world in some way, often in the form of control of rivers, weather, plants or animals. People will start praying to it as the "little god" or "kami" of an area or place and it will slowly forget it's old life, sometime even forgetting it was ever mortal. Some of the oldest kami have become so powerful, they can almost approach the power of angels.