The Soul is the immaterial essence of all creatures and the seat of both emotion and character. It is the immortal, supernatural spark that sets sentient and intelligent beings apart from base nature. Through it, a being can fulfill its potential and exist beyond death.
Despite their affiliation, spirits or ghosts are different from souls in that they are souls who use ephemera to exist in and out of the afterlives. A disembodied soul will exist in Twilight like a ghost or spirit, but abilities that work against these beings fail to manipulate it. High-ranking Ghosts, specialized Angels, some Chthonians, as well as demons and mages schooled in these esoteric arts can influence it, but learn that it is different from handling ephemeral creatures.
Souls appear without fanfare at the moment of birth and completely vanish at the moment of death. Most people do not even know they have one until they experience its loss. A person (any being), without a soul does not regain Willpower through surrender or rest, and her use of Virtue and Vice is reversed. Possession by hostile beings is easier and most supernatural arts, like Thaumaturgy, fail. Once the person's Integrity has been reduced enough, Virtue fails to provide satisfaction and the person is soon reduced into a catatonic mess, unable to spend Willpower.
Souls are not specific to a person. Should a mortal lose his soul, any other soul will suffice to restore him. Once a soul is replaced, the negative effects of soul loss quickly dwindle away.
If a person is brought back to life through magic, it does not possess a soul unless it has been stolen from someone else. The only ways of actually creating a soul (besides natural birth) are the Pilgrimage and Imperial Magic.
How souls are seen differs from species to species; as a result, many of the supernatural have a unique viewpoint of their souls and of the beings that their souls become after death.
As beings tied very strongly to the material, the Damned have little to no evidence of their soul left and see this as a part of their damnation. Common knowledge among the Covenants is that the Embrace drags back the soul as much as it can and fuses it with the Beast, where the remnant of the soul becomes the Man. The chains of blood that bind the vampire’s soul to his flesh are less secure than the spiritual anchor of a mortal, but they are more resilient. A vampires can absorb another's essence, including his soul, through Diablerie.
The Mekhet Clan see themselves corresponding to the Egyptian soul-structure as codified during the Middle Kingdom: A person consists of a Khat (a physical body), which serves as vehicle for the Ka (the "Soul of Substance"), which ensured survival. Furthermore, each person has a shadow called Khaibit, which is in turn connected to a Ba (the "Soul of Mobility"), which controls the movements of the shadow. Separate from both is the Khu (the "Spirit Soul"), which is inviolable and hosts the Sahu, the part that will eventually cross into the afterlife, provided that the other parts of it are unharmed. Beside these three pairs, each creature with a soul has a Ren (a True Name) and is animated through the life-force of the cosmos, Sekhem. Mekhet are creatures that have lost their Ka after death (usually through the Embrace) and have their Ba animate their body instead.
The souls of the Uratha contain a spiritual, predatory potential that awakens during the First Change. As they mature, this spiritual part becomes more and more potent, as Gifts are scoured into it and become an essential part of the Uratha's being.
In order to balance this spiritual part with their mundane roots, Uratha follow a codex called Harmony. If they err too much on the side of the spirits, they are transformed into Zi'ir, half-spirit abominations. If they err too much on the side of the flesh, they lose their supernatural abilities. While the Uratha's souls are more resilient against attempts to meddle with them than human souls, there are powerful creatures who can even affect them, like the Idigam, who can transform Uratha into Su'ur.
In Atlantean dogma, the Soul is the source of everything that makes humans humane and enables them to connect to the Realms Supernal. Some believe that the soul rises to the Realms Supernal after death, and reincarnates after purification. In academic terms, the Soul corresponds with the five Subtle Arcana and is connected to the Astral Space. Its connection to the body is governed by the Death Arcanum, meaning that those mages who seek to study souls often have proficiency in Death. It is that ineffable portion of a person that is responsible for her liveliness, vitality, curiosity, sense of wonder and connection to the world. The Weret-Hekau equate each subtle Arcanum with one of the Pillars recorded in ancient Irem.
The soul is also the portion of a person responsible for the use of magic. A mage that loses his soul immediately starts to Sleep again until he has his soul reconnected. Mages whose soul is damaged can turn into the Mad. A Mage can clip away a small part of his soul in order to create a soulstone, animate a Soul Golem or can shape his soul according to the attainments of certain Legacies in order to transform himself into something with more sympathy to the realms Supernal. Mages who tamper with souls are also called Reapers and are among the most cursed breakers of the Lex Magica. Several Left-Handed Legacies, the most famous being the Tremere, have committed themselves to the magic of the soul and how to harness it for their own purpose.
As fundamentally alchemic beings, Prometheans lack a soul and have to struggle to eventually regain one and become human again. This event - the New Dawn- is the goal of every Promethean who hasn't given into his Torment.
Arcadia has left its toll upon its inhabitants. Many Changelings who flee through the Hedge find that the Thorns have left them scarred and that some parts of their humanity have been cleaved away, filled with the Wyrd instead.
Ancient Irem discovered that the soul was not a vague, unitary life spark, but a complex mixture of elements with distinct characteristics. The Shan'iatu divided the human soul into five parts, called Pillars, that formed the foundation of human existence, maintained by the life force of Sekhem. During the Rite of Return, the mummy-to-be choose one Pillar that defines it before the Judges, forming their individual Decree.
Demons are devoid of a soul and have no particular interest in gaining one, unless they wish to obtain one for a quick Cover, and even then the soul is more of a disposable disguise (albeit one that, as far as anyone can tell, annihilates the existence of its former owner). In its place they have Primum, which is simultaneously the origin of their thoughts, reactor for their powers, and the shapeless state of their various forms.
The original soul of a Begotten has been obliterated during the Devouring. Instead, the Begotten contains one of the Horrors of the Primordial Dream within his form. The Begotten is permanently connected to his home realm through the connection to his Lair, but can also connect these spaces together, forming massive Hives in the dreamscape that can house numerous Beasts.