エーテル
Aether is an intangible substance in the Endless Ocean which fills the heavens and the void between the stars. The source of meteorological phenomena like auroras and thunderstorms, it is said to be the manifestation of divine will.
Apart from its immaterial form, aether is similar to air in many respects. It can give life to plants and animals, or fuel the heat and light of a flame. It is aether which gives fire to the sun, buoyancy to the clouds, and ferocity to a bolt of lightning.
Aetherstones
The existence of aether is proven by aetherstones, glowing crystals which appear in the clouds just before thunderstorms. These are hailstones which have been charged with aether, making its raw power visible and tangible to humans. Some make a sport of climbing mountains in stormy weather so that they can see and touch the crystals hovering in the air.
Aetherstones are prized by the Aetherwrights, who harvest them for aether on an industrial scale. Their swarms of airships and electrical nets are frowned upon by the other factions, who accuse them of tampering irresponsibly with the natural world and altering the climate of the Thirteen Lands.
Sacredness
Because of its association with the sky and lightning, aether is commonly associated with gods and divinity. There is a general understanding that aether is a heavenly substance and qualitatively different from other things in the natural world.
The Reliquary Church of the Domenican Empire teaches that aether is the sacred domain of the saints and transgressing upon it is a mortal sin. Because of this, research into burning aether as a power source is banned in the Empire.
Aetherworking
Aetherworking is the study and practical application of aether. It is a secret closely guarded by the Fraternity of the Aether, or Aetherwrights.
It is common knowledge that aether can be burned as a fuel or gasified to drive turbines. Through mysterious techniques, it can be turned into a glowing blue liquid called aetheric oil, which the Aetherwrights use for any number of things. The buoyant properties of aether can even be harnessed somehow to lift vast airships and entire islands into the sky.
Beyond this, outsiders to the Fraternity of the Aether can only guess at the possibilities. The principles of aetherworking are classified even to the majority of Aetherwrights, and only the Grand Magisters know the full extent of its capabilities.