The primary source of magical power the characters in this story would use. 

Aether comes from the carcasses of gods that have once roamed the Unified Realm. 

It's linked with a Witcher's Affinity, and gives her the power to manipulate and conjure her particular elemental affinity. 

Aether volume resides in our aether rose, or the core in which it's being circulated. 

A person who possess the power to manipulate his aether is called a Witcher. 

A witcher's mastery and power is measured through her aether circle, or the strings of spheres that acts as the medium in aether manipulation. 

Consequently, aether circle is also connected with our Affinity. Although a witcher can only have one main element, the greater her circle is, the more element she can influence on. That being said, our main element dictates our Affinity, so our ability to manipulate it is far greater and more versatile than the other elements we can conjure. 

Affinity is a person's individual and intuitive leaning on an element. 

We already know of the general four: fire, water, air, and earth. But other affinity exists as well, some can even be called legendary as it only appeared through myths and deep history. 

A 1st-circled Witcher wouldn't necessarily have her main element be reawakened immediately, though this case is rare. 

The greater our aether circle is, the stronger the connection to our Affinity as well. That includes the relationship between the aether circles within your body, so manipulation of both elements, even merging them, can be possible after practicing it. 

As I said, Witchers are the group of magically potent individuals who can manipulate the aether in their roses. 

Awakening of our first aether circle usually occurs during a person's teenage years. Somewhere between 12+. 

When that happened, the Imperial Monarch would send their help by giving the child, commoner or a noble, invitation to a three-year education in the Outer Academy of ODIN: Witcher's Academy. 

If the child, no matter his status, shows enough potential, then he might get recommended to the Inner Academy where the elites study the higher forms of aether techniques. 

Although a person who can manipulate aether can easily be called a witcher, but a "Witcher" is actually an official title bestowed by the Crown to individuals who passed the Imperial Examination. They are given certificates and a golden seal for this achievement, excluding some lands here and there. They're called "sir" as their status is akin to a knight, or the Imperial Warriors. 

Witchers who doesn't have their own affiliation can become a member of the largest magical society in the Unified Realm, called the Great Witcher Guild. 

One of them is Farris, the Fourth Realm. 

Although the terms can be used interchangeably, the distinction between the fief's multiple names lies in its formality. Farris is the official name of the land proper, where the Tower Lord possess absolute control second only to the Imperial Monarch. But there are several territories inside the Fourth Realm that remained independent, though they are also under the thumb of the Crown. The Fourth Realm is what we call of the entirety of this fief, though it's more of a title not a name. Commoners and hermits alike called the fief the Lands of the Dragon Tree, due to their belief that the Fourth Realm is once a lair of dragon goddesses who can control time itself. Some would call Farris, the Verelise Duchy, while opposition of the House Verelise would call it Erelian Tower. 

It's all confusing, but one thing is known. House Verelise has been the founding family that have taken the reins of the fief's history to the future. And now, their dynasty called the Erelian Tower, is the one who holds the greatest influence in the Fourth Realm. 

Marvius Y. Verelise II, is the current Grand Duke of Farris, but that's all. The Erelian Regency is the one manipulating the strings that holds the fief together, so the title of the Patriarch of the Tower is still out of his current grasp. It would be difficult gathering supports from strangers he's unfamiliar of to retake his rights, but that's his problem, not us.