Essence

Essence is a mysterious energy generated by the souls of all creatures, including demons and the Sovereign's Sentinels, despite the former being dead and the latter resembling machines. Most mortals and demons generate and accumulate Essence within themselves throughout their lives by simply existing, though at a very slow rate.

Uses For Essence
Essence is used as currency in most of the Five Realms. Anyone from mortals to demons to even fairies would accept Essence as payment for goods and services.

Essence can be transferred from one living being to another, if the sender and receiver are physically touching and both agree to the transfer to some capacity. The most Essence a living being has, the healthier and stronger they become. Having large amounts of Essence can result in increased longevity, and particularly knowledgeable magic users can even strengthen their spells and prayers with Essence after meditation and practice.

Many living beings, especially mortals, will subconsciously channel Essence into themselves as they grow older and develop their physical strength and mental acuity, which many impoverished individuals have deliberately trained themselves against doing in order to preserve what little Essence they have for use in purchases. This phenomenon ended up creating a situation where the poor and unskilled cannot learn and improve themselves as quickly as their wealthier peers, for they cannot boost their own development through the use of excess Essence.

Essence & Death
When a living creature dies, their body would release a fraction of the Essence they held as their soul escapes to another realm. This Essence would then be collected by the nearest other living being, which is usually their relative or whoever ended their life.

Essence & Demons
Demons, being made purely of souls, can consume Essence and use it more efficiently than mortals. This allows demons to absorb Essence by physically consuming the flesh of something or someone that produces it, which is an ability that mortals do not have.