Great Guardians are the sovereign lords of Fey that often hold lordship over whole regions of the world, commanding thousands upon thousands of Fey. They are second only to Wild Gods in power. Upon a whim, these fey could reshape the face of the world with their power. They often restrain this power, should the world be brought into a state of disaster, they are authorized to begin Reorigination, bringing the world back into a primal state, ready for new life to begin. This inevitably kills all existing individuals and forces them to return to Quintessence.
Great Guardians arise when a normal Fey lives for a certain length of time, and swells with enough power to evolve into a new state of being. Generally any Fey can accomplish this.