The soul is the metaphysical spirit of a mortal being and is the seat of human consciousness. It retains all the aspects that we consider makes us human, from personality to memories to how we experience the world around us. Souls are immortal and survives after death, when it is carried into the astral realm. This is contrasted with the body, which is mortal and has an expiration date. The body is the anchor that keeps the soul bound to the living mortal realm, serving as a container or vessel for the spirit. When the vessel dies, the spirit becomes unanchored and can no longer maintain its presence in the living world, forcing it to be carried off. The witch Dante has discovered a way to prevent this from happening, allowing her to extend her life in order to amass power.
By transferring her soul into the body of a living individual, Dante can take control of that body after her current form becomes old and decrepit. She can then live out the remaining years of that victim's life, with younger bodies naturally lasting the longest. Through this method, she can gain a form of immortality that extends her life indefinitely, repeating the cycle when it becomes necessary. However, this consistent transfer of the soul leads to visible side effects on the body. Each new body becomes deformed and disfigured after a period of time. This process speeds up with each new transfer of the soul, with every new form becoming more disfigured. This eventually leads Dante to resemble a hideous monster.
It is said that the forceful taking over of another individual's body to extend your own life is an evil act which darkens the soul, which is then reflected on the physical body. This is used to explain the effects. However, many people commit evil acts all the time, without the individuals performing them becoming deformed. Hitler has killed far more people than Dante and didn't wake up as a hideous freak, making this explanation nonsensible. How else to explain this occurrence?