First theory :
Killy is a human but immortal (like urashima keitarou), this may be explain why he seems invulnerable. There are alot event when Killy passes near death experience.

Second theory :
Killy is a cyborg(silicon life), a very old and advance one (from the age of lost technology?). However this theory is absurd, because it doesn't explain why Killy seems very hate silicon life, and try to kill them whenever he meet them.

Third theory :
Killy is a safeguard. This may explain everything ... (or not ?). In vol 3 the first encounter with Sanakan, Killy regained his function ... what function ? why did Sanakan said this ? also in vol 4, there's a controller said that Killy is secret agent of a pre safeguard. This theory support the Gravitonal Emitter Beam weapon he carrying around (similiar with Sanakan's, no ?).

Fourth theory :
Killy is human, but no ordinary one. Okay he is strong and age-less, but still human. That's until vol.3. when Sanakan shot some needles to his face. From all I know this needles is to make a safeguard out of a person body, but somehow this does not work with killy. Instead Killy possesed a ability of a safeguard (on fishermans village). This is perhaps why Sanakan said that Killy's register process is failure.

Fifth theory :
Killy is a game character, Blame! universe is just a game, and Tsutomu Nihei use Infinity HP cheat on Killy.

Another Question :
Some of timing process in this story seem not logical.
I understand that Killy spend 27460 hour (14 year) to recover from total damage in vol.9 after level 9 do something horrid to him.
But, in Vol.7 before Killy and Cibo meet Domochevsky, why they must spend 2244096 hour (that's 256 year) to just roaming around megastructure.

Anyone who understand this, or have another theory about Killy please reply ^^.

Here are my theories about Killy:

It's possible that Killy may not be as old as what many of us may think. Though he may be a secret agent of a pre-safeguard system, this does not automatically mean that Kily had existed before the safeguards. He may have simply been "hired" by the presafeguard system just as Sanakan became a temporary representative of the governing agency. Besides, how could something 3000 years old outlast the latest model safeguard? He couldn't have been that outdated... (But then again, Musubi kicked ass pretty well for a 3000 year-old safeguard prototype)

Killy is a former safeguard whose registration was erased along with his memory. All he remember's is the mission that was assigned to him: to find individuals carrying the net terminal gene. That's why he didn't know anything about his gun's origins.

However, when he encounters Sanakan she recognizes Killy as a safeguard. Notice that Sanakan immediately aims her gun at Cibo though Killy is the greater threat between the two (he tried to shoot her with his own gravity beam emmitter). When Sanakan has disabled Killy, she pumps him with those Insta-Safeguard Pins™ (which can turn humans and silicon creatures into safeguards) instead of obliterating him completely with her gravity beam emmiter. I believe she was trying to restore his programming as a safeguard.

Though Killy remains as an unregistered safeguard after that, he regains, or rather, remembers how to use some of his safeguard abilities. After that, he learns how to use his iris scan ability to identify humans, terminal gene carriers, silicon life forms and safeguards ("I've begun to understand what the insignia means."). Here are other enhancements he recieved:

Before: Killy still used binoculars to see objects far away (ex-log, vol1 ch4)
After: Killy uses his naked eyes instead (log57, vol9 ch7)
Killy: There's an exit 3000km ahead.
the guy in the Mori preservation pack: 3000km!! You can see that far!? That's an amazingly high resolution.

Before: Killy needed to used some sort of cassette player to make the builders stop (log7, vol1ch8)
After: Killy could communicate directly with builders (log, vol3 ch6)
Cibo: The builder!
Killy: It just came to put out the fires and make repairs.
Sutezo: You can talk to the builders?
Cibo: I've never heard of anyone who could do that.

theories about safeguards and silicon creatures:

Since the order stole their technology from the safeguards, their structures and program format are the same.
Cibo: What's this? The command format is like the safeguard. What the hell?

However, the silicon creatures were unable to perfect their silicon reconstruction High-level safeguards' have superior bodies because they aren't made of organs.
Cibo: it's so strange to have abody with no organs. It will take some time to get used to it.
Unlike their silicon creature counterparts, high-level safeguards will not die if normally vulnerable body areas are completely destroyed (Notice how many times Killy and Sanakan have been shot in the head?). Schiff, Pcell and Davinel on the other hand, are pretty vulnerable once the conversion tower in the area has been taken out. Perhaps the only exception to this would be the "new-model cyborg" within Toha Heavy Industries (it's regenerative ability surpasses all other silicon life forms).

Here's a wild theory
I think it's possible that most, if not all, high level safeguards have 2 forms, one is for carrying out "special" duties (their human form) and the other is purely for combat (mechanical/skeletal/winged). However, only Sanakan was able to make use of both in the series. Killy was unable to do so because he was not a registered safeguard, Dhomochevsky because he his area was cut-off from the Netsphere by Davinel and level9 Cibo because she was downloaded illegally and immediately disabled.

What is Killy?

I like your thoughts, G. Zeus. Awesome, someone I can agree with!

Here's what I'm thinking... Killy was a Safeguard, probably back when Safeguards were still humans, such as those guys in Noise. He certainly is 3000 years old 'cause Nihei himself said so. This is quite possibly, as his body is cybernetic, old parts can be replaced, and as far as we know, brain cells can live forever. Nihei mentioned in his artbook that Killy doesn't remember many things, though, because memories don't last forever.

So Killy's a cyborg that was once a Safeguard and now isn't. He's immortal, but that seems to be no big deal in this world..

The translation of cyborg to Silicon Life is incorrect.. If you look at the actual Japanese in the manga, the Silicon Life are called Silicon Life, not cyborgs.. I mean they are cyborgs, but that's a description, not a title. So when I say cyborg, I mean the actual word cyborg, no reference to Silicon life.

Maybe you're right about Killy's registration being erased.. Maybe that's why he's never brainwashed by the Safeguard. Interesting thought...

-Jenshin

Amazing !!

you guys have an excelent observing capability (what a word ^^ ). It takes me 10 times read Blame! to get a little understanding about it.

I have just found out about Nihei's artwook book translation over net, there are complete explanation about everything in Blame! altough my stupid brain can't really accept it straight away.

Anyway, there's one shot manga with title Blame (really), Nihei made. The main character is Killy too, but pure human. And the story seems far before the Blame! (I using "!" to difference them). is he Killy we all know ? is this Killy before he become a safeguard.

~thx to G-Zeus ... after reading your theory, now I'm more understand about Blame!~

Um, don` wanna spoil the topic but there was one like this allready...

I believe Killy is, as stated, pre-safeguard, some sort of uber program that was hacked together.

As you see in Noise, when people are investigating the Order's summonings and creation of Silicon Life, Musabi when she dies reappears in the net sphere, and as it holds her consciousness her body is recreated using the same technology as the silicon life just not corrupt perhaps. Would she be the same sort of thing? Pre-safe guard...? Just a thought.

Like redemption noted, it's pretty much a good assumption from what was shown to us in Noise that killy is an agent of the governing agency. During the manga they contacted him quite a few times and from the conversations they had you got the feeling he was working in conjunction with their wishes. Like the woman in Noise, he was probably originally a human who was imbued with a synthetic body made out of the highest level technology at the time which is why he seems to be a lot more enduring than most silicon life.