Soul

A soul is the immortal essence of a person. Ideally, it re-enters the reincarnation cycle upon the death of its physical shell.

Characteristics

A soul is highly malleable, but embodies a few core qualities that set it apart from the rest. For example, while Mizar's personality might fluctuate wildly from reincarnation to reincarnation due to the circumstances, whomever bears it will almost always be full of life, color, and energy.

A soul is incredibly valuable, and provides a huge burst of power to a demon that consumes one. There is little else that holds such power when it comes to making a deal. In many extreme life or death cases, a soul is all that can cut it.

However, consumption isn't the only practical use for a soul. Simply owning one's soul for their own can reduce the mortal in question to putty in one's hand. No matter how many times the original owner is reborn, the contract is binding. Therefor, selling one's soul is incredibly serious business. Making use of it is optional on the demon's part, of course, but it's incredibly rare for them to pass up the opportunity.

When a demon owns a mortal's soul, they become connected. Beyond just having the ability to control the mortal, the demon can often sense strong emotions such as distress across the link. It's also much easier for the mortal to call the demon's attention without the aid of a proper summoning. Additionally, the location of the soul in question can be easily determined through the link at anytime, while normally locating a specific soul would take considerably more effort.

If something leaves a deep enough impression on a soul, it can carry on as a metaphysical sort of trait, only visible to those with the sight. Henry's antlers are a prime example, being the result of a dose of Dipper's power.

Reincarnation

Before being reincarnated, souls enter an 'in between' phase. In this state, they are an abstract mix of all their previous past lives. Ordinarily, they feel a sense of peace and love, being intently connected to all who ever might have cared about them in a way that would never have been possible in the world of the living. In this state, it is possible for a being of higher power (such as Alcor) to separate an individual from the whole, and draw forth the persona of a specific life, bringing it to the forefront- though it takes a great deal of energy to do so.

A soul can be barred from the reincarnation cycle if it is either held captive by some powerful force or devoured by a demon. In the latter case, it will re-enter the cycle eventually, but not until after a period of time lasting up to at least a few centuries. Without the need of any intervention, it's also possible for a soul to remain in the world of the living by taking the form of a ghost until it is ready to pass on.

While possible, cross-species reincarnation is in fact incredibly rare (except in the case of mass extinctions). The case in which Mabel is reincarnated as a cat is a bit of an outlier. Additionally, most souls have particular instinctual 'preferences' when it comes to whom they will be reincarnated as, such as gender (more often than not, Mizar is reincarnated female).

Trivia

• Non-sentient species (such as bacteria and fungus) do not have souls.
• It is possible to survive without a soul, as some creatures, like Blighted Ones and horses, are born without souls. However, in most cases, life without a soul results in a zombie.