Raw Magic

Isen is a world with many magical elements, the most powerful of which is Raw Magic. Raw Magic comes to the world every 800 or so years in an enormous burst known as The Surge.
Raw Magic can only be used by rare people known as Wielders. A wielder can hold Raw Magic inside their body and, like currency, "spend" it to perform incredible magical feats. Once Raw Magic has been spent, it returns to the heart of Isen, and waits for the next Surge. A wielder can most easily perform feats that are within their personal nature. To do something outside of a wielder's nature takes more mental effort and considerably more Raw Magic.
If there are wielders present at the time of The Surge, then the immense burst is shared among them, making each wielder extremely powerful. Small amounts of energy are known to slip past the wielders, sending out "pockets" of Raw Magic far and wide across the world. These small pockets can be accidentally absorbed by an unwitting wielder who comes into contact with them, giving them a miniscule reserve of energy, perhaps enough to cause a minor rainstorm, kill a wild beast, or heal a wound. Many wielders throughout history have not known of their talent until they have done exactly this.
If there are no wielders present at The Surge, then the Raw Magical energy enters the world unleashed, and can cause globally catastrophic events, such as earthquakes, floods, volcanic eruptions, and other natural disasters.
Every time a Surge comes to Isen in this cataclysmic way, most humanoid races are brought close to extinction. With knowledge, history, architecture, and other advancements being lost or destroyed, forcing civilisation to start anew.
In Isen's many-millions year history, this has happened 47 times.
There are two immortal beings on Isen, called Anfer and Gilif, whose sole purpose is to search for wielders. Over the eons, these two beings have taken many forms, depending on the dominant species of the planet at any given time. In most recent history (some 10,000 years or so) they have been in the form of two human women.
Throughout history, Anfer and Gilif had been at odds with one another, regarding the wielders they find, and their methods for finding them. Anfer tirelessly seeks wielders out on foot, and prepares them to use magic in whatever way best suits their nature. Gilif prefers to hold a seat of power and have others search out wielders for her, then uses those wielders to further her own means. 
The last Surge (the year 800 AC) had 12 wielders present, from all corners of Isen. These wielders (commonly referred to at the time as "The Twelve") all made a pact to take their portions of the Raw Magic and hide away from the world. 
It is presently the year 1600 AC (After Cataclysm), and the next Surge is coming soon. Since The Twelve's pact, most people have forgotten that Raw Magic ever existed, many believing it to be merely a myth.