#this is very rough but ill probably do another round of edits before i post on ao3 in a few days

[thepetulantpen]

(Happy Valentine’s Day! Here’s my annual Saimota fic. As usual, keep an eye out for saimota fanart by @fancy-kryptonite​)

The anticipation leading up to Valentine’s Day is persistent, all-consuming, and, above all, irrational. It builds and builds past the point of overthinking and well into sleepless nights.

Holidays are always like this- a sort of performance anxiety to be happy, to make a day special. In a sense, it’s a self-fulfilling prophecy. He knows it can’t possibly be perfect, so he ruins it for himself before he starts.

It reaches a breaking point in the form of him mentally throwing up his hands, tired of debating with himself. There have been enough grand, somewhat ridiculous gestures over the last few years. No one is expecting him to do anything elaborate, least of all Kaito- who Shuichi finds sprawled out on the grass, a pile of books abandoned at his side. Unconcerned with the holiday a few days away.

“I was thinking we could try something normal this year.”

Kaito raises his head, not confused by the non-sequitur, but mildly offended- insofar as any of Kaito’s expressions can be called mild.  “I thought our other dates were normal?”

“Simple. I meant simple.” Shuichi can’t help smiling- only Kaito would consider scavenger hunts and secret love letters normal. He sits down beside Kaito, trying not to crush any of the books, borrowed far past their return date. “Easier to plan.”

Kaito looks relieved, and ecstatic- the latter of which is not particularly comforting. “Right, right. I’ve got the perfect thing.”

That’s fast, even for Kaito. Shuichi tries not to let it get to him- he hasn’t thought of anything specific yet. “Well, I figured we could each pick something- you take the morning, and I’ll take the afternoon?” Hopefully, that’ll give him enough time. “If you don’t mind. I mean, I could go first, if you’d rather.”

“Nah, I’ve got it covered.” He pats Shuichi on the back, with his usual lack of awareness of his own strength. “I won’t disappoint you, sidekick.”

I’ve really got to talk him into a new title.

He certainly sounds confident, but Shuichi has never known Kaito to not sound confident. He’d been thinking coffee or movies, but if Kaito has something perfect, then Shuichi has to step up his game. There’s only a day or two left- what could he do in that time?

“Shuichi? Did you hear me?” Kaito leans into his line of sight, waving his hand in front of Shuichi’s face. There’s no telling how long he’s been doing that for. He must take Shuichi’s expression for an apology, as he repeats himself, “I’ll text you the details. It’s a surprise, so don’t try to detect it, alright?”

Oh, good. Another thing for me to obsessively think about it. 

“I won’t, I promise.”

Kaito doesn’t look convinced. Shuichi can’t say he is, either.

…

Despite Kaito’s insistence that Shuichi would guess before they got there, the escape room ends up being a pleasant surprise. The waiting room is charming, filled with props to take pictures with and a massive winners board, and the hallway is filled with unassuming doors labeled with puns related to their theme. Their room is, fittingly, made out to be the scene of an old-timey murder- Shuichi and Kaito, wearing the deerstalker hats hung near the door, being the detectives called in to solve it.

It only occurs to Shuichi about halfway through that he’s spending Valentine’s Day rifling through blood-stained documents about a fictional murder while Kaito yells nonsense guesses to word puzzles from across the room. He wouldn’t have it any other way.  

“What if we arranged the dominos in a star shape? Is that anything?”

Shuichi glances up from the nearly illegible pages that have been unceremoniously shifted to his responsibility and finds Kaito juggling a tin of dominos and an armful of paintings that had once been on the walls. Those, at least, were meant to come off. 

“Uh,” Shuichi hesitates, caught between about three puzzles at once- one of them being Kaito, in general, “It couldn’t hurt?”

Kaito grins, obviously happy to do something. The paintings are scattered across the table, now crowded with other clues jumbled beyond recognition. From a glance, Shuichi can see that the lines painted on might actually make a star- but he doubts someone’s been assigned to watch the camera and wait for them to artistically arrange the dominos.

Kaito is not stupid. He’s practically an astronaut and, aside from that, he can be brilliant with people, far more insightful than Shuichi. It’s just- he tends to think in the abstract, approaching problems in a way no one else would. Meaning that the people who made these puzzles would never arrive at the solutions Kaito picks out. 

It doesn’t help that he refuses to use their hints, under any circumstances. The employee running the room had only egged him on by telling him no one had ever solved it in time without using a hint- Shuichi had accepted their fate, after hearing that. 

The intercom clicks on, the false cheer of their game master giving them a five-minute warning. Kaito scoffs, confidence never dulled, but the tension in his shoulders betrays him- his hands, over the dominos, have stopped, apparently realizing it’s not getting him anywhere. 

Shuichi had told himself, while they were waiting for the room to reset, that he wouldn’t take over. It’s supposed to be a casual game between the two of them, no pressure to win. Plenty of people fail these things, and they still have fun.

He has a feeling Kaito is not one of those people. 

“We still have plenty of time,” Shuichi assures, surprised to sound so confident, “I think the dominos are color-coded. Take these,” he hands off one of the papers, still running through combinations on the others, “and give organizing them a shot.” 

Kaito gives him a mock salute, but rises to the task. As predicted, he moves through the dominos quickly- giving Shuichi time to hurriedly unlock the next two safes. He’s had those figured out for a while, having thought he would have more time to guide them to the right answer. 

The solutions themselves are not terribly difficult. Nothing like solving crime, in any practical way, but they force him to slow down and connect all the pieces, adding up how every seemingly unrelated item fits together. 

“I’ve got it!” Kaito grins, the triumphant click of dominos set in the right position- a key to another code. “What’s next?”

“It corresponds to the filing cabinet,” he’s practically on autopilot as the clock ticks down, the flash of red numbers in his periphery, “I’ll take the desk drawers.”

It puts them shoulder to shoulder, both rapidly setting combinations and trading half-shouted numbers, unnecessary given their closeness. Kaito finishes first, so he gets to watch over Shuichi’s shoulder as he guesses the last clue. 

For a second, it looks like he’s gotten it wrong, that he’s failed them both, before the lights flicker dramatically. They all go out, save for a hidden projector that lights up one wall with the image of a wailing ghost- ah, he’d forgotten they were supposed to be avenging some spirit. He’ll admit, he wasn’t listening very closely during the introduction, distracted by Kaito’s grin as he took in the room. 

Kaito jumps about a foot in the air- clearly, he hadn’t been paying much attention either. Shuichi takes his arm, hoping to keep him from stepping on any of the discarded paintings.

“The necklace,” Kaito yells over the sound effects, wide eyed, “she wants the necklace!”

On impulse, Shuichi dives for it, digging through the pile they’ve accumulated, and tosses it to Kaito. He doesn’t present it to her so much as he holds it up as if it’s a crucifix he could use to exorcise her. The projection, unlike a real ghost, thankfully doesn’t mind his rudeness.

“I may finally be at peace.”

Figures that Kaito would be the one to bring peace to the ghost. It makes Shuichi smile, even as the lights are turned on abruptly, bringing an anti-climactic end to their adventure. The clock is paused at 17 seconds- not exactly a record to brag about, but he’ll take it. 

On their way out, Kaito elbows him to get his attention. “So, how long did you know the answers?”

Shuichi smiles and says, “Not long.” Which, judging from his expression, Kaito translates to “since we got in the room.”

Kaito doesn’t seem bothered, not like Shuichi thought he might be. If anything, he looks delighted. 

“We made a fantastic team, as usual. Under my guidance, of course.” He messes up Shuichi’s hair, a habit he didn’t bother kicking once they started dating. “With our smarts combined, we could do anything. You could be the first detective on the moon, you know?”

“I don’t know, maybe my calling is in paranormal investigations,” he teases, pretending not to notice Kaito’s grimace, “we could go on ghost hunts together.”

Kaito scowls, and Shuichi presses on, baiting the hook, “Unless you’re scared?”

“No man, nor beast, has ever bested me.” Kaito’s frown is close to genuine indignation, offended that Shuichi would consider him below ghosts. “Ghosts don’t even have bodies. I’ll take on a ghost, any time, any day.”

Luckily for Kaito, Shuichi thinks it’s unlikely he’ll ever have to deliver on that promise. “We’ll save that for another weekend, then.” He picks up the pace, leading the way, for once. “I’ve got something a little more romantic than a ghost hunt, this time.”

If Kaito looks inordinately relieved, Shuichi is generous enough not to notice.

…

Most people can tell when Shuichi is overthinking something. Most people know that answer is “always”. 

Kaito can tell when Shuichi is thinking of overthinking something. The calm before the storm, the buzz of energy that has him tapping his foot incessantly while staring into space. It started well before their date, carrying into the weekend of Valentine’s Day.

It all hits in the form of an over-packed backpack and piles of printed maps, stacked in the backseat. Shuichi has a schedule, complete with an annotated map of their hiking trail and final destination.

“We should make it there just as it gets dark enough to see stars. It’ll be a perfect view.”

The emphasis is obviously placed on perfect, Shuichi’s smile just a bit forced. Kaito gives the map a once-over- credit where credit is due, it looks as close to the perfect spot as you could get- and gives Shuichi a smile. “I’m sure it’ll be great.”

He may not be a detective, but it’s not hard to figure out that anything Shuichi comes up with will be incredible. It’d be difficult to have a bad time with Shuichi; any time spent with him feels like time well spent. The beautiful hiking trail is only a bonus. 

Kaito wouldn’t be surprised if Shuichi’s plans were flawless, every second mapped out. Every funny looking tree, every set of tracks in the ground- all set up for Kaito to notice, or for them to use as landmarks. Shuichi could say he’s set the stars on a timer, and Kaito might just believe him. If anyone could do it, it’d be Shuichi.

The sky, however, seems to have other plans. 

The clouds start rolling late in the afternoon and stick around stubbornly after the sun sets, filtering reds and purples through grey film. At certain angles, Kaito can see the moon in their gaps, but there’re hardly any stars persevering through. Dark grey shadows move over what might have otherwise been a fairly bright sky, now dimmed to a heavy static. 

It's remarkable in its own right, patterns of grey standing out starkly against the abyss of the night sky. It feels like the clouds are the only thing between them and limitless space, a simple barrier to surpass. Kaito only feels more drawn to it, eager to peel back the layers to see the stars for himself.

“I checked the weather,” Shuichi mutters, miserably, “I had three backups, and I was sure this one would be clear skies. I even looked up the constellations you could see from here-“

“That’s alright.” The grass has started to cool rapidly in the darkness, no springtime warmth remaining to greet them. Kaito lays out his coat to sit on, instead, and leaves Shuichi the more generous half. “It’s a great view, like you said.”

Shuichi squints at him, suspicious. “You can’t see any stars.”

“Stars aren’t the only thing I came here to see.” Kaito puts an arm around Shuichi’s shoulders, pulling against his side. He’s never embarrassed to be close to Shuichi, but he’ll admit he likes it best when it’s just the two of them, no distractions, no threat of self-consciousness. “It’s perfect.”

Shuichi looks down, hiding a smile. “Next you’ll be dropping cheesy lines with star metaphors.”

“There’s nothing wrong with star metaphors!”

He should be offended when Shuichi laughs at that, but he can’t bring himself to pretend. Shuichi’s laugh is reward enough- even if, objectively, star metaphors are among the best romantic gestures.

He’s still got work to do, as Shuichi sits silently beside him, staring at the galaxy print of Kaito’s jacket to avoid looking at the sky. It’s obvious he’s under the impression that he’s failed somehow, which just won’t do. As the hero to his sidekick, it’s Kaito’s responsibility to let him know he’s wrong- just, perhaps, not in those exact words.

Kaito nudges Shuichi and leans forward, craning his neck to get the best view of the clouds above them. “You’re underestimating the sky. Look, there’s always something beautiful to see.”

He points at the formations of clouds, shapes made of negative space against the moonlight. Their tops are highlighted by the escaping light, scattering over the uneven, cottony surface. Shuichi’s head tilts to follow him- it reminds Kaito of the escape room, focus taking over his expression. It’d almost feel out of place here, beneath the clouds with nothing of substance to analyze, if Kaito wasn’t used to seeing it all the time, for anything from figuring out a new coffee machine to spoiling a detective show by guessing the killer early.

“That one looks like a bear,” Kaito takes Shuichi by the shoulders, directing him to the cloud in question, “See? The other clouds are like the salmon it’s chasing.”

Shuichi doesn’t manage to sound very convincing, but he tries his best when he agrees, “I think I see it.”

“Hasn’t anyone ever told you you’re a terrible liar, Shuichi?”

Shuichi elbows him in retaliation, turning away from the stars to look up at him. He’s going for disapproving, but Kaito can see through him, far easier than seeing through the cloud layer. 

Somedays, it’s hard to believe that Shuichi bothers to hang around with him. Kaito considers himself good company, but for Shuichi? He’s not sure he qualifies- and yet here they are, under the stars. Or clouds, as it is. 

“One day, I’ll bring you to see the stars up close. We’ll go high above the clouds and into the night sky.” Kaito holds him closer, no longer interested in looking at the sky. “Just the two of us.”

“I’d like that.” Shuichi leans more into him, pushing for room on Kaito’s jacket. When he smiles this time, he doesn’t hide it. “I’ll have to consider space for next Valentine’s Day.”

He doesn’t sound serious, like he doesn’t completely believe Kaito will be able to pull it off. That’s alright- he has plenty of time to prove him wrong.

Kaito’s not being completely honest, anyway. Space isn’t his ideal Valentine’s Day- and it’s not an escape room, or star-gazing, either. It’s by Shuichi’s side, wherever that might be. If it’s watching reruns of mysteries he’s memorized the solutions to, or teasing him for his choice of black coffee, or just laying on the grass, staring up at the same sky.

The promise of another Valentine’s with Shuichi makes it all worth it. Kaito doesn’t need much else- though, he’s still looking forward to sweeping the clearance section of chocolates.

[gofancyninjaworld]

Meta: What rough beast slouches to be born?

Right, webcomic chapter 125 has raised quite a few questions about cyborgs and I purposely left it aside. Until now.  I’m sorry for the length, but I’m only allowed one ‘readmore’. :(

What we knew

Many moons ago for us, 9 or so weeks ago for them, Genos showed up at Saitama’s doorstep like a refugee from another world, telling a tale of destroyed towns, rampaging cyborgs, and desperate revenge quests.   It’s seemed rather far-fetched, particularly as not much has happened on that front.   Over the course of the story, we’ve had little bits of independent corroboration about the veracity of his story.  The town that he was born in was definitely erased from the map.  Yes, a cyborg is wanted in connection with the incident. 

But where is that guy? Does it have anything to do with the powered suit-flogging cyborgs seen early on the series? Does it have anything to do with the ‘glimpse behind the scenes’ chapter the manga offered us with Drive Knight (but no context as to how that glimpse fitted into the wider story)?  Come to that, where are all the cyborgs?

To start with, there are a lot of cyborgs of various sorts in OPM.  Quite a few moons ago, I wrote a bit about them, drawing a distinction between those who used parts to replace lost function and those who looked at it as a change of identity: “Is the Organization a Claw Analogue?”

 Chapter 125 has been surprisingly good about confirming some of what I surmised about cyborgs, but it’s brought some very good additional information!  On we go!

There are cyborgs; and then there are Cyborgs

Our ambassador through the world of cyborgs is new Neo Hero recruit Koko (Solitude), who modified his body for the world of cyborg fighting, only he was a little too successful and no one would bet on him.  We see him scanning various people and passing commentary on them.

The first to give him serious pause is Webigaza, who lost six months of life to getting her body modifications done -- no wonder she’s pissed off that her rival has self-destructed in the interim.

Koko is shaken by her having 71% of her body modified.

obsessive determination is terrifying to look at

Percentage body modification of the sort Koko is used to seeing, 30% maximum, you can do right here right here and now.  It’s equivalent to losing a leg and most of the other. Here and now, we can also do brain implants to control tremors or fits or some neurological conditions,  replace part of the heart, spine fusions, quite a few bits and pieces.  The sort of modifications Koko is used to seeing are very functional ones that make sense for someone looking to get an edge in fighting for money.  They’re also along the lines of what we’ve seen with One-Shotter or Death Gatling.

If you lose and replace all four limbs, that's 50% of your body modified. While quadruple amputees unfortunately exist IRL,  I don’t know if anyone has had the kind of money, physical fitness and pure grit to do that.  Nevertheless it’s not technically impossible. 60% sounds about right before you're now looking at breaking into the more vital parts of your body.  The point at which the risk involved just can't be justified in terms of restoring function or health. I’m emphasising that because I’m going to come back to this point.   He’s shaken because modifications that extensive aren’t about simply gaining an edge; they’re being willing to exchange serious bodily harm for serious power.  It says a lot about who Webigaza is.

Within the Hero Association, I think we do know a hero round about that 60% mark.  Jet Nice Guy comes to mind.  He sports an armored exterior, powerful artificial limbs (which will need internal reinforcement to not just rip up his body), but his innards are all human. After the way he started to bleed out after Nyan slashed him, I realised that the reason it looked like intestines when the Deep Sea King ripped him open is because they were... >.<  Sorry, dude. 

the worst of both worlds -- too modified to have an easy life, still too weak to deal with the real monsters that exist

Scary enough, but then the security staff come in to stop the kerfuffle that Koko and his buddy, Mars Leo, were causing.  Koko scanned them and was stunned into horror:

as disciplined and ruthless a pair of killers as you could never hope to lay eyes on.  Definitely not frothing at the mouth, these two!

These two have modified themselves so extensively they’re almost inhuman. 94, 95% body modification is equivalent to having only 3.5 - 4.2 kg of live mass left assuming an original live mass of 70 kg.  And, if the similar naming convention didn’t tip you off to it, it’s around the sort of hyper-extensive modification we see Genos having. [See under the readmore for a first-principles estimation I did a long time ago.]  Maybe Drive Knight too if he’s a cyborg.   What kind of power have they exchanged their human bodies for?  What kind of people are willing to do that to themselves? Koko is very sure that he does NOT want to know.

When he tells you who he is, believe him

That’s dating advice often given to ladies overlooking obvious red flags  but it goes with great force in OPM. ONE has characters tell us who they are early on, even if it doesn’t mean anything to us for a long time. 

And he’s had Genos be a particularly straightforward and truthful character.  He doesn’t always interpret things correctly, but he says it exactly as he sees it.  Looking at the way the high percentage cyborgs we’ve met thus far either be very inhuman looking or completely disguised as regular human beings,  he’s chosen an appearance that puts both his humanity and mechanical nature on display.

Something that the chapter has brought up that I've kept saying to people on the Discord and on Reddit: there is no medically justifiable reason for Genos to have a body as modified as he does.   Which Genos TELLS US for fuck’s sake.  His giant wall of text is a synopsis, no more and no less.

When he says that “...I asked Professor Kuseno to perform a procedure to modify my body. Then I was reborn as a cyborg for justice...”  (Viz)  “...I begged Dr Stench (sic) to transform me into a cyborg and I was reborn as a cyborg who fights for justice...” (Boon scanslations, who copied verbatim whoever did the webcomic version). It’s nothing to do with health.  Feel free to have whatever headcanons you like, but please don’t confuse them with the story.

But it doesn’t end there.  I look at Destro and Erimin and realise that there’s another perfectly truthful statement that’s been staring us in the face.

Genos knows. Why would he ask a mechanical engineer who uses a wearable battle suit and pilots armed drones to modify his body, let alone modify it to such an insane degree?  Because he knows that Dr Kuseno knows how to build cyborgs like the one who destroyed his town.

We don’t know if Destro and Erimin have any responsibility for the destroyed town, but someone of their ilk does.   Which brings us to a third nakedly truthful statement. When Genos talks of not believing that he could be defeated by anything other than the rampaging cyborg, he’s not anticipating winning because he’s suicidal.  It’s because he’s aware that if he’s throwing rock, so too is his enemy: mutual annihilation is the best he can hope for.

At least until he met Saitama. And started to hope for not mutual destruction, but victory (check the difference in chapter 108 of the webcomic).

a world away from the attitude of mutually-assured destruction he started with.

Stepping away from the text a bit, it casts a different light on why he’s been so desperate to learn from Saitama. Learning Saitama's secret is his balance-breaker. He wants something other than rock, that is guaranteed to smash whatever rock his enemy might throw.    But that’s not all there is.   As Garou said, once he discovered Blue Fire’s flamethrower, once you know how a freakish weapon works, you know it.  Any edge a new weapon might give Genos is liable to be studied and replicated  (see how quickly Dr Kuseno was able to reverse engineer and adapt the principles of G-4′s curving energy beams).   But Saitama’s strength is unphysical: no matter how closely you inspect his body, you can never relate the physicality of Saitama’s body to the power he can generate.  That unphysicality, that’s what Genos wants too.   It also puts in context why he’s been so fascinated by psychic power and wants to learn it if at all possible.

neat trick, I’ll take two!  Genos dodging G4′s beams in chapter 38, and putting the principle of them to good use in chapter 120

And finally, since in his world, knowledge is literally power, it gives yet another layered reason Genos is so determined to keep anyone else from becoming Saitama’s disciple.  If they learn his secret too, then the advantage he seeks will be lost.  (that it doesn’t work quite that way for Saitama is a fact for us to enjoy and for him to find out).

Nothing is as scary as a human being

Nothing is as scary as a human being is one of the things that Reigen says to Tome on occasion. It’s in full force in OPM.  Monsters may be strong, but they all live in the now.  Only a human being could have put together the Monster Association.   When it comes to cyborgs, their abilities may be inhuman but their thoughts, imaginations, morals and appetites are all 100% human.   It’s a terrifying combination.

There’s something I missed when I likened The Organization to a Claw Analogue. In Mob Psycho 100, the protagonists are children and they're fighting an organisation made up of over-grown children -- adults who have refused to grow up. In One-Punch Man, the protagonists are adults and the bad humans in the story are very much adults too.   With calculated cruelty and depravity to match. When The Organization bares its claws for real, this is going to get so brutal.

If Genos has not been standing still, then neither has his enemy.  From the manga, even if we hold Drive Knight blameless and independent of all this mess, his besting Nyan told us that cyborgs can indeed come crazy-strong and highlighted how much more work Genos had yet to do. It also highlighted how very clever and calculating cyborgs can be -- well, they’re human, duh!  If I was worried for his prospects then,  in the webcomic, Genos is nowhere near as psychologically, physically or emotionally ready as his manga version is.   And the guys who look to be his enemies aren’t going to be cutting him any slack.   They’re very real.  They’re not mad.  And they’re closer than he ever imagined.

Fighting monsters is barely adequate preparation for whatever it is that’s to come.

Whenever Genos gets dragged into whatever it is those cyborgs are up to  -- or runs into it, since he claims he’s still hunting the rampaging cyborg -- ‘rough’ doesn’t begin to describe it.

Extra Stuff

Edited from an answer I gave on Reddit to the question of how much of Genos was still organic about 2 years ago.  It’s unexpectedly relevant!

Short answer: by mass, under 10% , assuming he would have weighed  approximately 70 kg. By function, quite a bit.

 The long answer.

I’m going to write this starting from what is most readily observable and readily inferred to the least. In appreciation of this being a work of fiction that treats physical laws lightly, I too am taking a more-or-less approach and will keep technical terms to a minimum. I'm also not a medic and I don't play one on TV -- assume generous hand-wavium. Items in {curly brackets} are incidental notes you can skip.

Level 0: Canonically observable.  The least controversial observation is that Genos does have an organic brain. Genos does not live in a lab, but is able to live largely independently, including being able to eat whatever he likes with no ill-effect. Not just that, but he lives an active and hard-fighting life that appears to do him no permanent harm (I will return to this in a few paragraphs).  What can we take from this?

Edit: There is also ONE’s initial settings for Genos, which I quote here from the Hero Data Book

ONE: There's no need to visit Dr. Kuseno's place every time when his wrist break down, because he got his own spare parts at hand. Dr Kuseno's Lab is there In case for a big reparation job, a drastic upgrade or an examination.

It’s tempting to think that because we see that he definitely has a brain that’s all there is – the brain in a jar phenomenon, so to speak. Something a lot of people miss is that the spinal cord proper isn’t optional either -- it’s a core part of the central nervous system.  Spinal cords are a lot shorter than most people think they are, averaging 12 inches long for women and 15 inches for men.  The rest are nerve processes that can be cut and will regrow (within limits). We’re also happy to allow for nerves and their endings -- there must be an interface for the prosthetics so they're under the fine voluntary control that we see. However, that’s not all that there can be. The Cartesian mind-body duality is completely wrong when it comes to physiology. Our brains are intimately bound with our bodies and our bodies with our brains. So what does one need?

Level 1: Perfusion. This is the most obvious one. Without a blood supply providing oxygen, glucose and removing waste products from our brains, we have 4-5 seconds of consciousness available, 2-3 minutes in which we can escape brain damage and 8-10 minutes in which not to die. So, number one is a reliable blood supply.  Absolutely necessary therefore are a means of generating the various blood cells, perfusing and distributing them and disposing of damaged cells (red blood cells have a lifespan of 1-2 months). While not as acutely important, a self-sustaining blood supply is also the basis of a functioning immune system.  It's a bit of an oops moment when your super-killer cyborg catches a cold and dies.

Accordingly, bone marrow is essential as a source of hematopoietic (blood-forming) stem cells. A suitably reduced blood vessel and lymphatic vessel system is also needed to run the blood where it needs to go. {An awesome feature of living beings is that new blood vessels will be recruited to where they need to go and redundant branches pruned back, a process known as vascular remodelling}. A reduced liver and possibly spleen will be needed to appropriately destroy worn out blood cells. At least one functional kidney, in the role of producing the hormone erythropoietin, without which red blood cells will not be formed. Not essential: a heart and lungs, which he definitely doesn't have. How much blood is needed?  I’ll come to that answer once we’ve tallied how much body is needed.

Additionally, since part of perfusion is getting rid of metabolic waste, a liver and kidney will be absolutely indispensable.  

Level 2: Homoeostasis. A living organism has a very narrow range in which its internal environment, such as oxygen saturation, temperature, pH (acidity or alkalinity) amongst other things can vary without harm.

There are around 40 or so hormones, the signalling molecules that keep us going as functional concerns, regulating such things as blood pressure, salt/water balance, available energy, sleep cycle, body temperature, mood, immune system... the list goes on. Each has a stupid number of secondary functions and interacts with others in a ludicrous number of ways (note highly scientific language). Their levels vary and change on the order of seconds to hours. It's a good job that the main organiser of homoeostasis, the hypothalamus, is part of the brain. {Incidentally, this is why a brain-dead cadaver cannot be kept ‘alive’ on life support indefinitely – everything falls out of sync and eventually to pieces.} To do this artificially is to have your cyborg never leave the lab: if you're not constantly monitoring and adjusting levels, then they will die. Fortunately, as mentioned, a living, functional brain has the control network needed to keep everything working without the extensive and expensive effort. Just add air, water and food (in that priority).

At this point, we've already met most of the organs needed to maintain homoeostasis in their capacity of maintaining a blood supply. We need to add some bone, not just to serve as a niche (living environment) for the bone marrow and its stem cells mentioned previously but as a source and sink for minerals, the adrenal glands and the thyroid gland. Finally, one must not forget pancreatic islets -- or it'll be for nothing as he goes into a diabetic coma.

Level 3: Energy.   Speaking of food, a brain needs essential fatty acids for turnover and lots and lots of glucose for energy. It’s entirely possible to supply nutrients as total parenteral nutrion (TPN for short).  People whose digestive systems have completely failed get individually formulated TPN solutions, which requires that they spend several hours a day feeding it into their blood supply. Not something we see Genos do.  And yes, you heard it here: not everyone poops, but everyone sure as hell pees.  While a brain only weighs about 1.5 kg, it uses up about 500 calories a day as glucose, so 700 ish calories a day should suffice for all the needs of his live mass. This bears no relationship to the amount of food we see Genos put away on occasion. Why hasn’t he wrecked his liver in a matter of weeks? The answer would appear to lie in the artificial digestive system Dr. Kuseno has given him which turns food into biofuel. It must be patched into a feedback loop which allows it to only supply what’s physiologically necessary at any given time. Lucky for some!

Level 4: So how much body does that add up to exactly?  Nothing says you have to keep the necessary organs and blood vessel network the same size. With only a 1.5 kg brain to support, many can be shrunk a good 50% if not more. A total living mass of 7 kg would be quite feasible. We know from organ-on-a-chip experiments (and from unfortunate people who have lost part of their organs) that provided the essential architecture of the tissue is respected, they will work fine. Nothing says you have to keep them in the same place as the original organs were -- you can encapsulate it all in a can and shorten the nerves serving the organs to a more rational, manageable length. It's nice and compact and can be protected as heavily as the brain is.

Now we’re in a position to answer how much blood Genos has. There are about 70 ml of blood per kilogram of body weight, so at ~ 7 kg, we’re talking about 500 ml of blood. For comparison, the typical 70 kg person has 5 litres of blood. Why does this matter?  Because it allows us to answer a question many may be curious about: how often does Genos get hurt?

The answer is: Almost Never. With so little body, and with most of that body consisting of aptly named vital organs, even small injuries can turn catastrophic in no time.  Genos will bleed out with around 150 ml of blood loss, which is less than half of what is donated in a typical blood donation.  Horrible and dramatic as the smashes he gets into are, it’s more akin to a Formula 1 race car tumbling end over end and catching fire, only for the driver to walk out unscathed.  His cyborg parts are replaceable and can be sacrificed to protect what’s irreplaceable if need be.