I was actually having a theory that unification is actually two egos fighting for the body. If the shadow has a strong ego, they will "unify" with the body. If it failed, body is still human but no soot powers and shadow "dies"
Following this theory, Chris did suicide(maybe losing his Anthony form) so Anthony can live. If living dolls lived for the sake of their shadows, they will have little to no ego and will eventually think they are the shadow(then, unification). Shadows are partnered to living dolls to gain ego stronger than the living doll. Deviants like Kate might not need a host/living doll as she remembers from when she was formless, because she already established a bit of an ego back then.