Souls are the incorporeal life essences that constitutes part of the definition of an individual, it has never been stated or discovered from where or at what point in time one's soul originates.
Several species from animals from to mortals and other good beings possess a soul, although evil beings don't possess a soul which makes them free from to feel no conscience, without care and no remorse,
but there are an collective of rare demonic beings who are born with a human half and do also possess a soul. but souls are not completely necessary, as one would feel empty without a soul, but would still be able to live,
Soul Granting is often very traumatic for former evil beings mostly for those with a long history of evil acts.
There are beings that can create an energy comparable to a human soul and it combines with your personality the newly created human soul does not possess or grants new abilities.
The soul also can determine whether or not a creature is capable of fully appreciating the evilness of their own actions, with ensouled individuals tending to rationalise or deny their evil deeds,
Although it can take some time for to fully acknowledge the presence of their new found humanity initially simply being weakened, as time went on they can became increasingly aware of the guilt over their evil past.