Otherkin

Otherkin is a term for people who believe that while their bodies are human, their souls are not. Some believe that their souls are that of another animal, while others believe that their souls are that of mythical creatures. Coming to the realization that one's soul is non-human, is known as an awakening.

Otherkin (noun): A subculture of people who claim or believe that their souls are non-human

An otherkin's true form is the form that their soul takes. Their forms can be Elves, Faeries, Vampires, Fox, Lions, Phoenixes, ...even Dragons! True forms can be anything. For otherkin, they just happen to be non-human.