A void walker is the void element given coherent shape and a thread of agency, and there is nothing else to it. A living thing carries a soul and a shadow, the paired halves of its life-force, with a spirit between them to call itself "I." A void walker has none of the three. It is Nilus, the canceling layer of the Elemental Planes, arranged into roughly the size and the habits of a person. Where an elemental knight needs a suit of armor and a binding to hold its plane-fragment in shape, a void walker holds itself. Proportional absence, given just enough agency to wander, is the whole of what it is.
Appearance
You will most likely never see one. A void walker has almost no material presence, just a ripple in the air, the way shimmer bends a far road on a hot day, except there is nothing behind the bend. What gives it away is behavior. It is curious. A void walker drifts toward people, settles near a camp or a working party, and holds there, attending to the living in whatever way a thing without eyes attends to anything. It is not clever. No plan sits behind the attention and nothing is being worked toward. It is drawn the way a moth is drawn, and about as thoughtfully.
When it is bothered
The danger is in crowding it. A void walker does not strike. It un-makes. Press at it, corner it, give it reason to want you gone, and you begin to go. A person standing too close will flicker, stuttering in and out like a flame in a draft, and if the walker keeps at it they flicker out and do not come back. Gear goes the same way. A pack, a blade, a coat dissolves where it sat against the walker's displeasure. This is not destruction. The void walker takes the presence of a thing out of the world rather than breaking the thing, so nothing is left to bury or salvage.
You cannot talk your way clear of this, unless you are void-attuned. A shaper trained in the objectless feeling that Nilus answers can press something toward a void walker and get something back, though the exchange is thin: a pulse of curiosity, of irritation, of a wish to be left alone. There is no language in it and no mind to hold a language. Reading a void walker is closer to reading the mood of an animal, and the walker keeps fewer moods than an animal does.
Death
A void walker does not die so much as stop. When one ends, it dissolves cleanly and completely back into Nilus. It has no strands to send down the three death-roads and no true name to be forgotten, so nothing of it lingers and nothing of it haunts. The absence it was held in lets go, and returns to the absence it came from, whole and without a trace.