Like the Terror fold, the voiders are guards of the shadow realm. Except this time, they're a little bit more smarter.
Voiders usually use stealth and magic rather then brute force. But like the Terror fold, they use fear to their advantage.
Unlike the Terror fold, Voiders are actually souls that are already dead. Zealot gets several dead souls from Hades and converts them into brainwashed Voiders. Which is why Voiders usually have amnesia and know nothing else but to contain and kill.