(Base idea is taken from Yu Yu Hakusho; kind of a nice way to describe it so like, why not?)
Power and magical abilities are derived from the levels of energy found in a soul. This energy, or “spirit energy”, is supplied by the universe and is a fundamental aspect in the structure of a soul. All living organisms have some amount of spirit energy since they contain a soul. Artificial life is the only exception. Even the gods have something similar to spirit energy as they are tied heavily to the universe itself. Levels of spirit energy can be broken down into the following grades: E, D, C, B, A, and S. Above that is considered god-tier.
Grade Levels for Earth:
Almost zero: bacteria, viruses, microorganisms, etc
Low: plants, insects, fish, etc
Normal: average mammals (including humans)
High: humans with 6th sense/affinity with supernatural; low-leveled fae, mermaids, weak werewolves and vampires, etc
Average fae and human-based supernatura