I was really thinking of Dark Domain as more of a third or fourth tier skill, because it does seem a little powerful. Though I also thought about adding a drain effect.
Perhaps I'll make disorientation my second halo...
Black Aura: By activating this halo, Retta's entire body is covered in a dark aura. While this aura is visible to others, it does not cause others any difficulty in seeing her. In this form, Retta's speed is increased 1.5 times and whenever her aura touches someone, it drains their spirit essence. This essence is converted into essence that Retta can utilize as her own, restoring a small portion of her own essence.
PS, I really want to call this skill Darkening... not related to the canon one. But I figure that could be confusing.