The human body is not fully equipped to deal with having pieces of it excised and replaced with cybernetics. There is always a period of adjustment while the mind comes to grips with the neural interface pathways required to use the new implant. This often causes a feeling of dysphasia, where the user’s mind does not recognize the implant as part of it, and perceives its actions as alien or controlled by some other. Through the use of anti-dysphasia drugs and subtle tweaks in Angel code, most of humanity learns to deal with their cybernetics. The adjustments become harder and harder as more of the body is replaced with cybernetics. In some cases, the mind within the increasingly inhuman body fractures, and begins to create the Other that controls the cybernetics. When this happens, the cyborg often goes on a killing rampage, requiring an intervention from the Cybernetics Enforcement division of the local police department. These people are known as Headcases.
In other cases, the human mind controlling the body shuts down entirely, no longer able to accept the changes in its reality. Usually this means the person dies, but in some cases the body continues to function, supported by its cybernetics even while the meat dies around them. Control of the body is subsumed by the Angel within, which in most cases will continue to try and accomplish the tasks that its previous owner would have done on a daily basis. These creatures are called Zeroes. Most Zeroes are harmless, but in the occasional rare instance the Angel somehow achieves sentience, possibly because of the greater demands placed upon it without feedback from the previous owner, and goes rogue. In these cases, the consciousness controlling the Zero is totally alien to what humanity understands and its motives are inscrutable. All that can be assured is that the Zero will take any steps required to preserve its own life.