Remnant

''"What is this?" Steven asked, poking at the holographic vial floating in the air.''

"Afton Robotics' most secret research discovery," Digi answered grimly, "Remnant. The essence of life in transmutable form..."

This is for the AU version of Remnant, not the canon Remnant of the FNAF games.

About
Not much is known of Remnant save that it was discovered by Afton Robotics and is able to be removed/transplanted into humans and animatronics. One known method of transfer is via a device called the 'S.C.U.P.', constructed by Afton Robotics and housed in the Sister Location facility.

Remnant needs to be kept at a sustainable temperature that allows the substance to be malleable but not liquified. Overheating Remnant neutralizes its effects of granting 'life' to animatronics.

Uses
The current known use for Remnant is granting 'life' to animatronics, giving them an awareness far greater than artificial intelligence alone can account for. Based on behaviors of animatronics affected by Remnant, it is possible that the original Fazband is also implanted with Remnant via having children stuffed into their bodies and ground up by the endoskeletons' motions.

Remnant appears to be more easily collected and extracted from children.

Activation
Remnant is most active in the young and begins to grow inert as the vessel grows to maturity. As Remnant becomes inert, the soul disperses into the body and becomes 'anchored' to the body, released only by death. However, Remnant can be reactivated by exposure to spirits or large amounts of spiritual energy, causing a person's soul to migrate back into the liquid. Locations that are haunted or stained with large quantities of Remnant are capable of reactivating Remnant in older persons, allowing the old to regain the ability to be possessed or transfer their souls into other forms.

Copying
Remnant can be used to overwrite another's soul via copying by injection. A person can take a portion of their own Remnant and inject it into another's body whose Remnant has been weakened or extracted. The injected Remnant then begins to grow with experiences and 'take over' the host body at the cost of reducing sanity in both the original person and in the host. The host also loses old memories in exchange for the knowledge in the injected Remnant taking their place, and eventually the color of the host's eyes change to match the color of the original person. In this way a person can be 'copied' into a new body, as cloning only affects DNA and not Remnant.

A person whose Remnant containing their soul has been extracted but not replaced with any other Remnant -making them soulless- will rapidly lose their sanity when out of proximity of the removed Remnant. This causes drastic shifts in behavior and personality, and causes a number of mental instabilities. Eventually, the body is unable to maintain life without the soul and the person dies, often by self-inflicted harm.

Trivia

 * Lucian was just young enough at the time of Afton's experimentation that his Remnant could be collected. However, the extraction was only partially completed. What was obtained was processed into data form, creating the foundation that would become the Lucian Master File and Digital Lucian.