I’ve been toying with the idea of a Ghost in the Shell-style campaign using Cortex.  Scattered throughout the core book and the Serenity material is much of what you might need to develop a setting similar to Shirow’s world.

First thing that is necessary is to have some kind of idea regarding cybernetics.  For systems like Cyberpunk and others in the cyberpunk genre, there is a tendency to get very detailed with the type of equipment that you’ve bolted onto yourself.  This isn’t really necessary:  most of the cybernetic enhancement can be covered by a few Traits, well described.  In essence, you have two things cybernetics would do, systems mechanics-wise:  increase your attributes, provide an existing trait, or provide skill emulation.

CYBERNETIC ENHANCEMENT (d2-d4):  You’ve have work done to improve your body’s natural characteristics — maybe it’s a kinesthetic monitoring system that enhances your inner ear, or sensory buffer that pushes data to the brain at a faster rate giving you a better Agility or Alertness; maybe it’s artificial eyes or ears that give better vision and hearing, adding to your Alertness; maybe its an adrenal boost that aids in your natural Strength; maybe it’s a drug shunt that adds to your Vitality or Willpower tests.  Whatever the system, it hacks the meat to push it to its limit.  You can take this multiple times, to give the boost across abilities.  Gives another die for tests involving that particular attribute.

METACORTEX (d2-d6):  This is a cybernetic uplink that conencts the user’s mind to the internet, or whatever you’re calling it in the campaign.  It doesn’t boost the intelligence of the user, per se, but instead gives a die bonus when doing an Intelligence based skill like Knowledge, Scientific Expertise, etc.  It allows you to find the data on the wb/net/cyberspace, and use it.  It doesn’t make you a surgeon, or an astronomer, or make you an expert in the paintings of Matisse, but you might be able to fake it.  It could also give the Enhanced Communications Trait at d6 (Because of the nature of the cyberpunk genre, I’d say just have this cost the equivalent of a d4 trait as an add-on.

Another Cybernetic Enhancement might give a Trait, instead — bionic legs might give a Fast on your Feet, but don’t offer much else in the way of enhancement; a Vehicle Interface would give you the Born Behind the Wheel Trait that is good for any vehicle; Eyes and Ears might provide Enhanced Senses; nanobots designed to strip toxins and disease from the body might provide a combination of Hearty Constitution and Fast Healing — or possibly Immune, depending on the nature of the cybernetics.

Cut down to the most basic levels, these are really the only Traits you need for the basic cybernetics.  To tailor them, you can take Complications specific to the technology.

Maybe your iBrain only works on the AT&T network, and as a result, you can’t always get a signal or fast throughput, you could take OUT OF NETWORK (d2-d6):  Depending on where you are, the GM might have you incur a die penalty, added to the difficulty of whatever Metacortex-based test you are rolling.  (“Dammit!  I’m only getting one bar — I’ll never get the recipe I need for this casserole in time!)

Maybe your strength benefit from cybernetics is specific to a single limb (“My right arm is the best prosthetics money can buy!”), and can only really be used for crushing or punching, but you can’t benchpress a ton if only your right arm from shoulder to hand is artificial.  Take the cost of the enhancement dow a die step, but note that it’s only go for such-and-such.

The real issue would be full body prosthesis — essentially, you would have to build the character as usual, but with the CONSTRUCTED Trait and NONHEALING Flaw — you require repairs after damage.  You might go so far as to have something like ROUTINE MAINTENANCE (d2-6):  If the character doesn’t receive routine service, their body is prone to breakdown or malfunction.  At d2, thy require service every six months, d4 monthly, d6weekly.  If they aren’t maintained, they must roll an EASY RESISTANCE for the first time period (for a d4, the first month), then +4/per period (AVERAGE for two months on a d4, HARD at three, etc…)  If the roll have failed, they have their die rating added to tasks as their system break down.  On a botch, they completely fail and cannot operate until repaired.

I think the tricker elements are the full body prostheses of GITS, where there’s enough of their biological bits and bobs left that they have to eat, but have to have mainenance, where they are resistance to disease, but the meat bits can still get sick.

Still ruminating on this…