A/N: It's no coincidence that the first part of this chapter bears a striking resemblance to Unvirtuous Treaty Ch 2. Leave it to 9S to intellectualise the concept of blue balls.

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4. Derivation

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A whole week has come and gone since 9S's and 2B's fateful encounter with the white boar. As necessity dictates, much of this time is spent convalescing at the Resistance Camp. This means that no progress has been made on any important front, which only compounds 9S's already heightened state of restlessness.

In light of 2B's injuries – which have put her out of commission for several days – their mission is postponed for later completion. This leaves 9S to play grudging errand boy in the meantime. (Just because his partner isn't available doesn't mean he's incapable of work, as Command not-so-kindly points out.) In between the tedium of ferrying supplies and answering requests that involve the correction of inputted commands or hacking open someone's overcomplicated security lock, he lets his mind wander. Invariably, it rewinds to that incident: his and 2B's moment of accidental intimacy.

Now a whole week later, he's still obsessing over it. Replaying it on an endless loop like some broken record. Scrutinising every frame down to the nanosecond lest he missed some subtle but crucial detail. Dissecting every snippet and nuance of dialogue in the hopes of uncovering some hidden meaning, some unspoken implication.

It's a stark contrast to 2B's complete disregard of the matter.

One would imagine that an exchange of such an intimate nature would change his dynamic with 2B. But nothing's different. 2B is no closer and no more distant than before, ever teetering on the knife's edge of her strange ambivalence. In fact, she doesn't seem to acknowledge that the incident took place at all. Is she feigning ignorance, or has she legitimately forgotten about it?

Whether it's thanks to avoidance or obliviousness, she won't be discussing the matter with him anytime soon. Which raises the question: does he even wish to discuss it?

One thing is certain to him: he does and doesn't want another encounter like that with 2B again. That was a gross lapse of judgment on their parts, a moment where they both lost control of their impulses. Ironically enough, their roles were reversed: he, the more emotional one, had attempted to be the voice of reason, or at least until reason had fled out the literal crevice window. Were it not for the Pods' (un)timely intervention, how much further would they have gone?

If she approaches him in that manner again, he'll have to refuse her – as much as he loathes the very idea. Will her flirtations be genuine, born of actual interest in him? Or will she be acting under some kind of influence, as he's suspected all along? How can he, in good conscience, accept her advances if they are always accompanied by that sense of wrongness? That would be purposefully casting aside intuition in favour of selfish desire, and he won't allow himself to sink to that level.

Yet he cannot stop thinking about what happened. He cannot smother the lustful sound of her heavy breaths, the intoxicating taste of her lips, the delicious friction of her body sliding against his—

Dwelling on it only exacerbates his frustration. How he hates this obsessive nature of his. It attests to the weakness of his resolve, letting these base, human urges overrule his rational mind. Left unchecked, they form the worst kind of distraction, surfacing at every possible and inopportune moment. Describing the feeling as an itch at the back of his head is an understatement. It's more like his internal processes have spiralled into a slow but uncontrollable meltdown, leaving him to burn up from the inside out.

Maybe he ought to stamp it out of his system. He considers recalibrating his personality matrix, to excise that part of himself that brings about these unwanted feelings. (Perhaps humans would describe their equivalent procedure as a self-directed lobotomy?) But that's a very drastic, not to mention risky venture. While scanners are well-versed in maintenance tasks, this is something that requires a healer's level of expertise. Without their precision or knowledgeability, he might end up damaging or corrupting integral parts of his personal data.

Can he consult a healer for this sort of thing, anyway? Not only does it seem frivolous – it's not contributing to the war effort, after all – but it's almost certainly illicit. If emotions are already a taboo subject, what's to say of those that arise from fraternisation, which is more taboo still? There's no way he can obtain official approval for this. He'll have to get it done under the table, that's for sure.

Or he can resort to more, ahem, crude methods. If he can find some relief through manual stimulation, he might be able to think more clearly. Any escape from this infernal fixation is more than just welcome; it's urgently needed.

Yet he baulks at the idea.

Here he is, the prime of android engineering, intending to make use of his near-perfect imitation of human physiology for this depraved pursuit. It's downright insulting to his origins, the purpose of his creation. Androids have not been fitted with human-like parts for their entertainment, but as a tangible, incarnate reminder of the ones they serve. By abusing his bodily functions in this manner, would he not be dishonouring their gods on the moon?

Not to mention it's wrong to reduce 2B to some kind of masturbatory device. Even though she visited these feelings upon him, he's the one at fault for harbouring them, allowing them to reach critical point and thus drive him to insanity. So why should she have her image sullied just so he can alleviate his goddamn sexual frustration – the inevitable end-product of his stupid obsessing? Doesn't she deserve more respect than that?

But despite his reservations, the urge eventually becomes so maddening that he gives in.

The act of self-pleasure is one he absolutely cannot afford to be caught indulging in. So he takes meticulous care with his preparations, mapping out an appropriate time and place to conduct his business. Once situated, he undresses, trails his fingers southward and brings up the relevant memory. He reimagines 2B's close, almost suffocating presence, those powerful, electrifying sensations as she ravished him. This has the effect of triggering the same intense, pleasurable responses as during the event, if somewhat muted. But they're enough. Only mere minutes later, he is spilling into his hand, calling out 2B's name in a shaky whisper.

As soon as the euphoria dies away and his pulse and breathing decelerate to more reasonable parameters, he is overcome with shame.

Water might wash away the evidence of his indiscretion, but it cannot scour his mind clean. He feels so intractably dirty. Was this moment of temporary relief worth the sin of defiling the sanctity of his human likeness, of 2B's pristine image? After all that agonising and tearing through his misgivings to finally carry out the deed, he's rewarded with an extra layer of guilt and self-disgust to add to his tally of mental burdens.

Wondering how he will get through this, 9S skulks back to camp.

The moment 2B enters their shared room, 9S knows something is wrong.

Before slipping into rest mode two hours ago, he was convinced of her good mood. Last he checked, she had set aside her usual aloofness to hold a friendly conversation with a couple of Resistance members. Now, she doesn't resemble either of the hot or cold personalities that he's familiar with. Her body language is defensive and skittish, a far cry from her usual confidence. The way she holds the door's frame for support – even going as far to lean back against it – is a sure sign of weakness.

As always, worry overtakes him, along with a healthy dose of suspicion. Were it not for the uncanny timing, 9S would've guessed that 2B is suffering from some motor control malfunction. No, this is something else – perhaps the transitional phase he hasn't yet observed between her two personalities?

From the way 2B glances around the room, 9S deduces that she's searching for something. Her gaze follows a somewhat predictable route. Interestingly enough, it skips the busier areas, like the piles of storage containers and shelves packed with various Resistance paraphernalia. When she spots 9S, her body stiffens and her teeth sink into her lower lip.

So, she isn't expecting him to be here, still asleep. Or pretending to sleep, in this case.

Virtuous Contract materialises behind her. 2B reaches for it, grasping the hilt in a reverse grip. At the sight of the familiar white katana, 9S's pulse quickens. He's had a close shave with the business end of that blade only three missions ago, back at the machine factory. However, he and 2B are not within enemy territory now – the very opposite, in fact – and there is nothing that would justify the use of weaponry.

But as 2B braces the sword tip against the ground, it becomes clear that she is forgoing its typical use in lieu of a balancing prop. With uncharacteristic gracelessness, she stumbles across the room, her gaze tracking 9S's stationary form all the while. Once her hand lands on the wooden desk in the corner, she braces her weight against it, letting Virtuous Contract fall to the ground with a faint, negligent clatter.

"Pod," 2B calls out, noticeably out of breath, "is 9S in rest mode?"

Pod 042, who is hovering atop 2B's right shoulder, turns in 9S's direction. "Analysis: Unit 9S's external state would suggest that he is undergoing rest mo—"

"Confirm his actual state, please," she interrupts, a desperate edge to her demand.

As Pod 042 approaches, 9S hastily pulls up a mental command prompt. Faking rest mode beyond a superficial level is impossible, and his duplicity would become obvious once the Pod scans him. However, he can alter the variable it will access. Since Pod 042 is a combat-oriented model – to compliment 2B's designation – it lacks the ability to perform checks more involved than fetching a text display. With this in mind, 9S switches 'active mode' with 'rest mode'.

Having now situated itself above his head, Pod 042 begins the scanning process. An unpleasant, icy tingling permeates 9S's circuits, spreading across his nervous framework like a particularly noxious gas. He's certain there aren't any YoRHa units who enjoy being the subject of this particular Pod function. Although it comprises part of normal maintenance routine, the discomfort it brings about tends to be muted by one's limited sensory capacity. Unfortunately, 9S doesn't have the benefit of that dampening barrier now.

The scan lasts for an agonisingly long minute, as if each passing second contains an eternity of its own. To avoid detection, 9S must actively suppress his thought processes. He cannot afford to have Pod 042 pick up any inconsistencies in his mental state, lest it become suspicious and alert 2B. That would, for certain, put a stop to whatever she's planning to do in private.

"Analysis: Unit 9S is confirmed to be in rest mode," Pod 042 finally states, before floating back to 2B and reclaiming its position above her shoulder.

Shoulders sagging, 2B lets out a sigh of ostensible relief. "Thanks, Pod."

Then she turns to face the desk, and her right arm shifts towards her front. 9S deduces that she's reaching for something. But because her back is now obscuring his view, he cannot see what it is – or where she might be retrieving it from. He rules out the possibility that it's an item on the desk; they haven't used that piece of furniture upon their arrival. Not to mention that it's 9S who carries their on-field necessities in his scanner's pouch.

Lowering her head, 2B moves her other hand to the back of her neck – the area dedicated to installing and modifying external chips – and practically rips off the dermal panel. This exposes her entire chipset. 9S squints under his visor, trying to work out what 2B is doing without making any movements that would give him away.

She pulls out a large, inexpensive-looking chip. From what 9S can discern, this isn't a standard chip of YoRHa or Resistance design, which are more compact and require less pins (even those of the budget variety). Then, with her right hand, 2B brings up a similar chip. After some fumbling – thanks to her lack of coordination – the new chip is fitted into its designated slot, and the dermal panel replaced.

At first, nothing seems to happen. 2B goes still; her likeness to a statue would be perfect if not for the uneven rise and fall of her chest. However, as the seconds coalesce into a minute, the tension leeches out of her frame, and her breathing assumes an easier, controlled rhythm. Leaning her head back, she lets out a quiet hum, revelling in some secret contentment that only she experiences.

Another minute passes before she turns in 9S's direction once more. Disappointment wells up inside him; he fails to see any evidence of the removed chip either around or on 2B herself (insofar that his feigned immobility would allow, anyway). Bending down to pick up Virtuous Contract, 2B dematerialises the katana with a flick of her wrist. Then she shifts her gaze onto 9S, a strange smile blossoming across her face.

"Rest well, Nines," she whispers. Her voice contains not a trace of ingenuity, only warmth.

She heads towards the door, inverting her step as to quieten her footfalls. It doesn't take her longer than a few seconds to exit the room, shutting the door behind her.

9S allows his artificial lungs to expand and draw breath again. Then he stifles said breath, lest the hysterical laughter that has bubbled up inside him escape. It's possible that 2B still stands within earshot, after all.

The culprit was illegal chips all along. Illegal fucking chips. Mixed in with some kind of positive mood modifier. How could he have missed such an obvious answer?

Rolling over onto his side, 9S contemplates what to do with this new information.

He needs to get his hands on those chips, for no accusation can be founded without tangible proof. But frisking 2B for them – assuming she stores the chips somewhere on her person – is too risky, even during a maintenance session. Not to mention 9S is loath to invade her personal space like that. Maybe she keeps a stash of the stuff in a more permanent location? Searching her room on the Bunker may prove fruitful, though the element of risk is no less great. Partner or not, he is bound to rouse suspicion by barging in without permission, especially with so many potential witnesses around to catch him in the act.

Yet 9S is already formulating plans. How would he sneak into 2B's room unnoticed, and when would be an appropriate time to do so? What would he do once he has procured the desired chips? Dismantling the things to find out how they work and making further investigations are foregone conclusions, of course. Should he confront her about them?

How would 2B react if he does?

Troubled, 9S shifts from side to side, unable to find a comfortable position. However good his intentions, he would be going behind 2B's back – again! – to try and solve a perceived problem she had not requested his help for. Not to mention he would be taking it a step further, by violating her trust in order to steal from her.

It's wrong on so many levels. Despite that, one thing is clear:

2B cannot continue to use those chips.

Given their likely bootleg origins, there's no guarantee of safety. Is inducing a temporary, artificial state of happiness worth the gamble of harmful side-effects? The emergence of her erratic behaviour is already an indication of this. What if it becomes more erratic? What if 2B actually hurts herself in the process? What if she kills him by accident, an action that she's come perilously close to carrying out before?

Worse yet, what if she loses her identity, everything that makes her so... wonderful?

At this thought, 9S feels his black box seize against his chest, and heat prickles at his eyelids. Pulling down his visor, he finds himself surprised at the amount of moisture that has gathered there, enough to trickle down his cheeks. A quick scrub across his face wipes it away. Then his jaw clenches shut as he gnashes his teeth.

No. He cannot – will not – allow 2B to destroy herself like this, consequences be damned. He will not stand idly by and watch the one he cares about more than anything else fall apart. Yes, the decisions that hang in the balance are difficult and morally questionable, but he will not back down from them.

Whatever the cost, he will fix her. Starting with—

—ransacking her room.