Umbra Castra of the Darkness is the second in command of the Altusian Brotherhood. He was the Dark Warrior that discovered that Infra was the new Chosen One, and he has since joined his side betraying his other comrades.
Umbra is very casual, laid back and rather cocky. However, like Infra, he is a master of alien psychology possessing extraordinary charisma and rivaling his leader in ability to exploit others emotionally.
It turns out that Umbra Castra is an actor Vaikan robot remotely controlled via microwormholes by one of the last living Omni. Umbra's physical self is deep within Debesis in a stasis chamber filled with some of his dead brethren. The robotic avatar is his outlet to the outside world.