Soul

A soul is the eternal life essence of a human or witch, which resides within a physical body while they are still alive. After their physical body dies, or is destroyed, the soul continues to exist, and typically moves on to an afterlife realm. While a spirit can be corrupted and destroyed, a soul cannot.

History
The soul was originally designed and collectively by the Architects sometime before the creation of humanity.

Characteristics
Souls are magical by nature and could be used by supernatural creatures to cast spells or to increase their power. While the soul can sustain great damage and be drained of energy, it cannot ever be destroyed and will always repair itself over time.

Usually, souls leave their vessels when they die, being taken to their final place, but they can be removed by force, leaving their owners soulless. Though the soul is essentially a human's life essence, it is possible for their physical body to continue functioning without it. When this happens, the soulless body's spirit will retain the person's psyche, emotions, intelligence, motivations and such, except there will be a total unable to process love and pain, and right and wrong.

According to Amun, the soul acts as a shield against the corrupting effects of Hell. Without a soul, most spirits that enter Hell are corrupted into demons.

Deals
In exchange for a soul, a demon can grant a human any desire they wish. At the moment of the human's death, the demon usually comes to collect the soul.

Power
To perform certain spells, witches must tap energy from their soul. While the soul is known for being an extremely powerful energy source, harnessing this power is dangerous and can easily destroy the person entirely if not performed precisely.