MEC

The Metabolic Extension Controller is the device, or sum of devices, necessary to sustain the existence of a Revenant It was developed from the Jarvik 2000 ventricular assist device, and added to over time by various medical teams.

A standardized MEC design would only come about fully in the last century of the Millennium; in its completed form with basic features, it's composed of a secondary heart, a pacemaker and defibrillator to restart the natural heart, a "brain pacemaker" (neurostimulator) to restore the patient to a conscious state, and (in the Millennial Kingdom) a precise transcranial probe to eliminate the ability to conceptualize pain, made necessary by having to allow the patient to not perceive the pain of Hell lest insanity occur after only a few minutes.

Add-ons includ a gold wire lightning rod from the base of the skull to the thigh or heel, adrenaline or other drug injectors to maintain homeostasis or boost performance, a NFC serial interface to allow direct control of equipment, and so on.

Variants

"Heavy MECs" would undergo a much more invasive procedure in order to preserve their brain, head, and as many remaining organs as possibly (at minimum, usually, one of the lungs).

The Only Light mass-produced a semi-external metabolic extension controller to install on their Relentless troopers, reverting ther minds to bicamerality and allowing them to operate with minimal cognition (enough to follow orders) but enhanced performance until their joints and muscles broke down from overuse. Due to their appearance, they were often referred to as "fast zombies", despite not being actually undead.

The precursor to the MEC was developed by CATS during the Tribulation by modifying existing Jarvik 2000's, but did not feature any neurological enhancements, and was only issued to the Foreman and a handful of special agents due to the extremely high cost of manufacture.