Essences are magical beings that exist without a physical body. They exist in various forms and have different origins. However, no essence can survive for long periods of time without physical form, which is why they possess other beings to survive.
Life Essences are artificial life-forms comparable to a human soul. Some are originally created by the powerful Demonic Alchemists for their own personal gain. A well-made life essence can possess and animate any person it wishes. although it is toxic and eventually fatal to the soul of the person it possesses.
Many essences only search for independent life and only possess others in order to survive. Life Essences can be trapped in an Essence Bearer for their disobedience.