The Ever-Dying are humans, which they are called because – from the viewpoint of magical beings – they’re dying from the moment they’re born.
They have no magic, nor any ability to use it. This isn’t a matter of effort, or intelligence; humans can’t wield electric shocks like eels, either.
Curiously, though the Ever-Dying may not be able to use magic (or even perceive it), they are capable of cross-breeding with almost all the magical races, producing Kin, for the most part, refers to human wizards – that is, humans with something else in them allowing them to do... More. This is unheard of, and greatly puzzling to those with the minds to wonder at it.
Why? Nobody knows. How? Nobody knows that, either, but humanity’s ridiculously effective reproductive ability is the reason Kin are so numerous that they had to receive their own category.