All magic flows from the titans, or at least from their destruction. In a world where a titan has fallen, and life has taken hold, a transformation takes place. As life forms move through their cycles they unwittingly absorb remnants of the titans power. As the power gathers the organism becomes more aware of itself, and its relationship with the world. It also becomes addicted to the accumulation of this power and the awareness that flows from it. If it gathers enough, if it develops enough, well we call those few rare examples gods.
For millennia that was the way of the world.
The dragon gods were the first to change the nature of things. When their world came crashing down they saw the potential end of all life and vowed that should life recover they would ensure it could defend itself. They guided the evolution of all life that followed, seeking to create a self-aware mortal species. With the emergence of early humanity, they finally succeeded in their task.
The downside was that a species already self-aware had a head-start towards godhood. There came an overabundance of new gods which proved a both a boon and a bane to the older gods, for while they had an inexhaustible food source they also had a lot more competition.
As humanity advanced the new gods upgraded their followers, ranting them the loci. A spark of arcane energy that, in concert with self-awareness wouldn’t just attract magic, but would actively create it. Loci can be passed to offspring along family lines and is often known by its more common names of soul-seed or primal spark.