Etherious are a race of Demons that were born from the Books of Zeref. They are made completely of Ethernano, with the exception of E.N.D. and were thus dubbed by Zeref as the "Etherious".
Description[]
Etherious is the given name to the subspecies of the Demon race that were created from the books made by the Dark Mage Zeref. Unlike the Demons that inhabit Galuna Island, not all Etherious possess wings and they do not all possess Human forms.
The Etherious can also, at any given time, be transformed back into their book form by their creator, Zeref, and will all cease to exist if he dies.