Just a quick thing I made up. This is my fur Rain if he was in Undertale! He is a ghost who found a skeleton uninhabited and found that this was the corporeal body he were looking for! Little did Rain know that it was left over from a human who was captured and experimented on... His magic is what caused the physical changes: the fur and the anatomy.
He found out the origin of his new body after he bonded with it, and thus couldn't leave it. Out of respect for the deceased, he always makes sure to try and keep out of battles and not seriously damage himself.