Similiar to Chrono String Engines, the H.A.L.O. System is used to control the probability constant of Chrono Strings. Through this system, the probability of gaining energy from Chrono Strings can be directly interfered with, allowing a much larger amount of energy to be drawn out. It utilizes a quantum computer to scan the minds of the Angels to allow them to accomplish this. Appearance-wise, it takes the form of a white halo above the pilot's head.
However, if the scan level is too high, it can cause the Angel to go into a trance state, where their body will enter a dangerously unstable condition. Also, if the flow of the scan is reversed, the system will backfire into the pilot's mind. If this happens for only an instant, the Angel will be forced into a comatose like state, though nothing not treatable by a UPW medical facility. Any longer exposure to a reversed scan will likely have irreparable consequences to both the Angel's mind and body.
In TCY 417, Noa developed an AI system that adapted the H.A.L.O. System so that the probability controlling aspect no longer depended on the pilot, and was rather handled by an AI. This system is used in mass production Emblem Frames like Holy Blood, allowing them to be piloted by anyone.