Magic in my game is only NATURALLY accessible to a race of witches/wizards and a race called the Ahriman. They call upon an invisible energy from the world which they use to cast spells. No humans can use magic NATURALLY as their body is not in-tuned with this energy as mages and Ahriman are. When mages and Ahriman die, their energy and body is absorbed into the ground. Overtime that energy can turn into crystals that humans can use as energy, such as electricity, light, synthetic magic, daily use. These crystals are like batteries so they only have a certain lifespan. The brighter the crystal, the more juice it has. In the current timeline, all witches/wizards and Ahriman have pretty much gone extinct(to the people's knowledge). The humans have been harvesting an unknown crystal they call Draodite which allows them to mimic magic like the ancient wizards of old.