Spirits, or also commonly referred to as Mystics, are living beings from another dimension that traveled to Etaera some time 70 years or longer before the main storyline takes place. For over two decades, dimensional rips in space-time allowed creatures from either dimension to jump to the other. Some say mystics came to our world as watchful protectors, whereas others view them as demonic and evil. All will agree that most of their actions, makeup, and abilities are justly scientifically inexpiable.
Although all spirits are classified as creatures, not all creatures (by far) are spiritual beings.