Essence is a Essential Aspect of a character; It is a life-force representation used to make Bonds and Attunements, Pacts, and fuel Augmentations and powers through Mystic Offerings of sacrifice and Ritual. It is reflected in a character’s Aura.
Most living things have a natural Essence Pool based on their Order of Being that binds them firmly to a continuum, while others are more connected to the Aether or even tied to the Void or the The World Beyond. A setting, locale, and/or race can limit how a character may spend Essence at the time of Character Inception and beyond. Some have specific uses of their initial Essence dictated or adjusted.
Starting: (based on Order of Being of your species/race; typically 5) + Weave Factor (factors in Sanity and Charisma) @ Character Inception
Adjusting: Permanent Sanity and Charisma changes recalculate the Weave Factor and trigger a moment of Actuated Awareness. It can be sacrificed for many gains, including those of Pacts, signs/portents, as well as deep Bonds and Attunements. Additionally, there are dark arts and strange ways of transferring it between beings. Certain events may trigger a spontaneous change:
Weave Factor = Half of Sanity OR Charisma (round down/whichever is highest) + Proficiency Bonus
BASELINE Example: Sanity 11 | Charisma 15 = 5 + (15/2=7) + 2 = 14
Weave Factor: Sanity * Charisma
BASELINE Example: Sanity 4 | Charisma 4 = 5 + (4*4=16) = 21 @ Character Inception