so Killy is a cyborg if i am correct. a very sturdy and lasting cyborg, almost bordering on immortal, but the problems are with his memory.
Zouichi is also a cyborg, and what happened in chapter 28 of Biomega, i have to admit i didn't get much of it but; it seems to me he has to stalk around that big cable base thing for quite some time... like someone else.
my theory is: lets say after Zouichi completes his goal, or fails, his body is either stored in some sort of containment thing or he is just forgotten somewhere in the world. then the world gets back up (correct me if i am wrong but i believe that Biomega happens before NOiSE, so i think that the events and humans and world of NOiSE is after the events of Biomega and the world is back up running more or less) and makes Builders, things go wrong, stuff start to expand, etc you know the story. what if the Governing Authority found Zouichi's body or was given it by Toha as a trade deal to leave them alone. they would then base Killy, Sanakan and most of their cyborgs on that design. to me it makes sense
(sorry if my writing is hard to get or for any miss-spelled words. first post! wooo!)

Given the size of the megastructure, I wonder if it was just a coincidence to begin so relatively close, almost beside, TOHA industries.

Well, I think Synthetic Human is totally different from Cyborg.

Uhm.. I believe you just marked the difference between the two. I think it's just too soon to enounce this kind of assumption. But you just remembered that Killy was human once while Zouichi was born/build as a synthetic human.
In the corner of my mind I secretly believe that Biomega probably is placed way before Noise (IF the Blame saga has anything in common with Biomega). Neither the Netsphere nor any kind of connection to a different realm/reality is mentioned. Seems like the starting point here is the seek of immortal life.



Anyway.. it's just too soon for me

I really dont get why a lot of people here are so obsessed with this topic.
To my mind its totally obvious that Biomega and Blame are two different stories and wolrds.
Just think of Noize and you know it !
The only link is Nihei himself.

But then again a lot of people dont seem to get that Nihei doesnt work very linear in a lot of aspects.

The similarities are quite natural for any artist, i think.
Also people (read: buyers) often expect artists to be samey over and over again. I think its called style, isnt it ?!

Nihei has explored already a VERY broad spectrum of cyberpunk !
How many possibilities do you have in cyberpunk/transhumanism ?

Cyberimplants, biotech, nanotech.

And a lot of it has been done already.
But still he added a whole unique universe (or even mulitverse if you want) to it, that is totally his own !!
Whats really special about Nihei, is how surreal everything is he does.
How visual.

Bah, I think they're related. Zouichi is obviously Killy's father.

Despite the fact I've read Blame! several times, I don't ever recall hearing something about Killy once being human... what's that about?

Cyborgs are people with robot parts, synthetic humans are... well... people... that are synthesized, presumably artificially.