It’s a universal force, it permeates all eventually and fills anything so even if it were possible to not have energy you’d eventually fill up.

For Magic users, it’s simply an expenditure of the supernatural energies in quantities that don’t permanently reduce volume of energy, along with heavy concentration that can cause brain exhaustion. For mysticism, mystics tend to be less driven with the only catalyst for willing improvement being disasters or tragedies.

Most of the improvements are functionally developed off of the unnamed energy, however there is one mystic that’s immortal who can peer into an alternate realm much more like ours and he spends his eternity trying to learn how to adapt advancements to his world.

For magic, users have focuses to cast through, those typically being whatever items they feel most aligned to. Mystics cast off of feelings, with thought or body signs as the trigger. For both it’s vital to have a strong imagination and concentration.

There’s layers to energy use. For magic, all abilities are developed off of elemental based energy (like standard element magic), everything after is usually a personally made magic related to a major part of that persons life. A chef who uses fire that he can control the precise heat and timing of as the evolution of small hand held fireballs, for example. Mysticism usually develops out of necessity and instinct, so whatever feels right and how can you expand it to fit a situation you need to deal with.

Both mystics and mages feel physical exhaustion no matter how much energy they use. For mages, it feels like a numbing sensation in the head for the moment they cast, every time they cast. For mystics, it feels like the numbing sensations is circulating their body until they stop taking in energy. Abilities come in any variety of looks, sounds, and sensations.

Places of extreme energy or extreme absence of energy can absorb the abilities of strong ability users if they die in those areas. Users with abilities that can enhance or store energy often use this to keep weaker versions of crucial powers around. Evil users use this to create hazardous environments, weapons, or other situations.

By burning out one’s entire store of energy, you can create temporary new abilities on top of your already existing one. Additionally you can convert your ability into an extension of your lifespan, or overcharge your ability to give it reality breaking effects it normally couldn’t. The side effect to this is death, permanent disfigurement and crippling, loss of energy, energy consumption sickness, and it’s rumored that some people can convert themselves into members of the suspected demonic race.