Aether is an energy source found in The Shattered Isles that causes them to float and powers behemoths and weapons.
Aether was used by the great Aethersmiths to forge massively powerful weapons. These weapons were used against the Behemoths, who in turn consume aether with every island they conquer, becoming ever more powerful.
The aethersmith is closing up shop as you walk up, having just come from the dock. “Little late to be getting back from the frontier, isn’t it?” he smiles, wiping sweat from his brow. “Too late to fire up the forge at any rate. Swing by tomorrow and show me what you found.” He turns to go inside when you produce the glowing arcanite from your pouch, energy swirling and seething beneath its surface. He stops mid-stride. “Where did you… Well, it won’t do you much good without the–” You retrieve the fractured behemoth horn with your other hand, letting the light of the setting sun glimmer across its razor-sharp edge. The smith tucks his rag in his belt, waving you into the shop. “Alright, slayer,” he says, grinning as he grabs his apron. “It’s going to be a long night, then. Help me get the fire started.”