Most times, she goes to Null. Not always, of course--Null comes to her room after Zodi's been put on lockdown for eviscerating a few irritating scientists, giving the kind of punishment Zodi fears and craves in equal measure.
And there was that one delicious evening when Zodi was laid up after winning a hard fight and Null had come to her hospital bed, kicking out the doctors before crawling under the covers to give Zodi a very personal reward. Zodi holds that memory closer than anything, even closer than her first kiss.
Still, she usually comes to Null. Zodi always keeps her ears pricked for the buzz of her communicator or the buzzer in her room, waiting to be summoned--she never makes the first move, even when she wants to. She can imagine a lot of wicked things, but trying to picture that level of presumption makes her head hurt.
It can be a little irritating at times, having to stop training or torturing or whatever the hell she’s doing at the moment, maybe even being called away from sleep or a meal. But Zodi won't lie and pretend she doesn't savor the long, slow ascent through elevators and stares, the tension that builds so beautifully with every floor.
Her primary destination is Null's office, to be tipped over the desk or spend hours with her head buried in Null's lap. Trips to Null's private chambers are less common, and they always make Zodi's heart beat a little faster.
Today is an apartment-day, and she's too excited to really notice the longer journey. Security is a bit of a pain--Null's place is surrounded by a tangle of armed security, electronic surveillance, and runes that give Zodi a headache as she passes--but she's done this enough for the process to be relatively smooth.
A guard gives her a knowing smirk as he steps aside to let her through one of the final doors, and Zodi smirks back, making a mental note to find an excuse for ripping his lungs out later. It's his own fault, really, for not figuring out that an endlessly blank expression is the best way to stay alive in a place like this, among his betters.
Null's apartment is dim, a sharp change from the bright fluorescents that wash over the rest of the building day in and day out. She makes a point of keeping the lighting low, saying that it helps her head after a long day.
And it reminds me of home, she'll say, smirking. Zodi has never asked how much Null's appearance is a joke at humanity's expense and how much is based in reality; frankly, she doesn't give a shit. Null is Null, she's the first face Zodi remembers seeing and she'll be the last Zodi sees when she dies. Everything else is just so much nonsense.
Even in the dim lights, Zodi's eyes are keen off to see the faint shine of expensive-looking paintings and jewel-studded statues scattered across the room, the glint of diamonds and rubies scattered idly across the mantelpiece.
Null gets a kick about keeping beautiful old shit like this locked up in her apartment, of taking these things humans might kill each other for and not even giving them proper lighting. The thought always makes Zodi smirk to herself.
She's distracted, however, by the sight of Null sprawled across her couch, having exchanged her ever-present suit for sweatpants and a hoodie. Zodi's keenly aware of what a rare sight that is, how few people get a chance to see Null so vulnerable without dying instantly and messily, and it makes her feel warm like few things ever do.
Null's got her head buried in some kind of high-tech pad, fingers blurring through a tangle of holograms. Zodi can catch glimpses of letters from a language she can't read--a language that no one on Ear can read, probably. Null's eyes are narrowed in concentration, and it's hard to tell whether she actually sees Zodi standing there or if she's just fucking round.
Zodi waits until she can't anymore (it's always so much harder to wait with Null). She gathers her courage and clears her throat: "You wanted to see me, Ma'am?"
Null glances up from her pad, blinking, before her lips curl into a sharp little smile. "Ah, Zodi." She taps a button--Zodi thinks she sees an image of something's head exploding on one of the holograms--and sets the pad aside, flicking it off. Her eyes gleam in the low light, red spots dancing at where her pupils should be.
Zodi lets out a long, slow breath. Even now, even after all the things they've done, there are still moments when Null makes her feel nervous. She can face down an army without flinching if Null asked her to, but sometimes just looking her in the eye is too much to bear.
"I take it the mission went well," Nun says, rising from her seat.
"Yeah, I--"
"I'm glad to hear it." Null circles her, feet silent on the apartment floor. She looks at Zodi carefully, assessing every strength, every weakness. Checking for damage, maybe, although whether it's to Zodi as her property or Zodi as her...something else, Zodi doesn't know. She doesn't like to think about it.
Null rests a hand on the small of her back, pressing ever so gently against the skin. She could break Zodi's spine with one shove, but instead she just reaches down with her free hand, tracing it along Zodi's hip. Zodi squirms just a little, breath catching.
"Clothes off." Null's voice is soft as a breeze in her ear, but it sets Zodi into motion like a starting gun. She tugs her shirt up over her head and wriggles out of her shorts, folding her clothes much more neatly than she ever would in her own room.
She can feel Null's eyes on her backside as she bends to set her clothes and lets herself savor that feeling, the complete, inescapable weight of her creator's attention. Krisa says that the way Null looks at them sometimes is creepy, but Krisa doesn't know what the fuck she's talking about.
Zodi straightens up, rigid as a soldier. For once in her life, she doesn't talk--Null doesn't care when she talks, not really. Zodi's not naive, she understands that. They don't need words, anyway.
Null's hands scratch so gently over her breasts and Zodi arches into the touches, feeling a weight she didn't even notice was there sliding off her shoulders. Null chuckles in her ear, low and dark and lovely. Her scent--blood and ash--fills the air, and Zodi inhales it greedily.
She can feel Null's hands start to shift, touching all the seams and creases, all the places she knows that gives Zodi the most pleasure. And she knows, the same way she knows from the beginning, because she's the one who designed Zodi, penned every line of her genetics to create the perfect weapon. She knows Zodi, who she is and what she needs, better than Zodi ever could.
Isn't it sort of like fucking your mother? Krisa had asked, in one of her more aggressive moments. And Zodi had just laughed and told her Null wasn't their goddamn mother, because it was easier than admitting that's the best part. 
"Bed." Null orders, pulling away. Zodi trots her eagerly, palms sweating like it's the first night all over again. She can't help herself, sometimes.
Null knows that, of course; she might have even designed Zodi that way. Zodi can see it in the way she smiles once they've entered the bedroom, waves of red light from the fire hovering in the corner washing over Null's face.
That fire shouldn't exist, but then again, neither should Null, or Zodi. Her mistress has a habit of bringing about wonders like that.
"Undress me." Null spreads her arms like shadowy wings.
"Yes, Madam Null." Zodi gently, gently removes each piece of clothing, setting ever the humblest one aside with care. Things should feel more equal when they're both naked, but Null is so beautiful it's hard for Zodi not to feel small in her presence.
No one makes her small, ever, except for Null. The feeling is, if she's honest with herself, intoxicating.
Null lies down, sprawling elegantly as a queen across the pillows. She smiles up at Zodi--a smile that's as hungry as it ever is, but warm, too, different from her regular knife-slash. "Well?"
Zodi forces herself to breathe as she crawls onto the bed, doing her level best to keep her tail out of the weight. It's an effort that will wear on her, but she knows it's worth it.
She thinks that Null might be the only person she touches, ever, without violent intentions. Her skin is impossibly smooth and unnatural, pulling Zodi's hands across its silky surface with a force like gravity.
She worships Null with her fingers and tongue, savoring every inch of her like this is the first, the only, time. She takes time to suck each nipple long and slow, to map the curves of Null's thighs, to lose herself in the landscape of her thighs the way she loses herself in a twitching, bleeding corpse. And she seeks out places like the spots between Null's fingers or the jut of her knees, places she's learned were sensitive through long, careful study.
Null's breath starts to hitch a little at her touch, and that makes Zodi's breath hitch in response. I'm doing that, she thinks, with the same childlike wonder she'll watch herself feeling as a body topple at her feet. I can do that. I can do things like that. There are moments when it doesn't seem real.
She holds off on visiting Null's cunt for as long as she can stand it, wanting to draw this out for as long as she can. Eventually, though, Null's sounds start to become more demanding, and Zodi hurries to plunge between her legs.
Null's cunt is hot, like a blast of heat against her tongue, hot enough that it almost hurts. Pain is so rare for Zodi and she chases it eagerly, digging her fingers into the sheets so they don't accidentally jab into Null's hips. She knows there's nothing she could do to hurt Null, not really, but she still wants to hold onto what little control she can.
She eats Null's cunt like she kills--hungrily, joyfully, and with well-honed accuracy. Null once said she was among the great pussy eaters she's encountered over the centuries, and Zodi has done everything she can to be worthy of that title.
The process is at once impossibly exhilarating and familiar in a way that resounds at her core. Zodi knows how to track the noises Null makes, the precise shudder and ripple of her flesh, the way she sounds as she builds and builds and builds. 
And yet, she's always caught off guard by the first burst of heat on her face, like fire on her tongue. She has actually burned her tongue, sometimes, and the tang of cold cream on it afterwards felt like a blessing.
She holds Null through the shudders, their bodies rocking together like wave after wave. Null snarls in a language Zodi doesn't know, snarling words that slam into her brain like punches, and holds the sound as close as she does the taste of Null's pleasure.
When it comes to an end, there's quiet, except for Null's soft, sharp pants. Then she says, with only the faintest shake to her voice: "More."
And Zodi gives her more. Until her jaw aches and her limbs tumble, until her mouth feels scorched from the inside out, until her head swims and her tail aches, until her own trapped desires make her hips feel like they're about to shatter, she gives more, and more, pouring herself into Null's need.
She owes everything to Null, after all. Null gives Zodi the breath in her lungs and the blood washing her hands, Null gives her the heat of a warm bed and the grim satisfaction of a screaming night.
Zodi will never be sure if Null sees her as a person, but she knows that Null sees Zodi as hers. And that must make Null Zodi's, too, doesn't it? In her own way?
These are the thoughts that swirl through her head when Null finally lets her rest, slumped and stained against the blankets. She can feel Null looking down at her, hear Null draw one long, deep breath after another as she claws her way back to composure.
"You did well, girl," she says.
Zodi can't hold back a little moan at the praise. "T-thank you, Madam Null."
"Always so greedy." Null laughs a little to herself. "Come here."
Zodi does, gathering every fragment of strength left to push herself upright and crawl to Null's side. She feels herself being pulled into Null's lap, a quick and dangerous hand slipping between her thighs.
It doesn't take long, a fact that she's faintly embarrassed. Not nearly embarrassed enough, though, to keep from wailing like a stuck pig or a security guard, head thrown back as she explodes.  
If she shrieks Null's name, the sound splitting from her like a prayer or a plea, Null doesn't say anything. Zodi's grateful for that.
Eventually, she crumples forward, feeling Null gather her up gently and just...hold her. Hold close, close enough that she won't fall away, but also not tight enough to hurt. And there's nothing wrong with hurting, Null has hurt her plenty on rougher nights, but the gentleness--that's something else entirely.
She closes her eyes and lets her head fall carefully onto Null's shoulder. In a few minutes, maybe less than that, Null will order to leave, and she will. She'll totter out of there, naked, and force herself in her clothes before making her downstairs.
She'll wash off Null's smell and go train or whatever, sharpen her blades, maybe just lie on her bed and look at the ceiling for a while. If Krisa comes by she'll crack a dirty joke and tell her to fuck off and not look the snake in the eye. She'll dream of blood and Null and all the things she can taste, but never have quite as much as she wants.
But that's a few minutes from now, a few hours, a few days and centuries down the road. In this moment, she lets Null's arms wrap around her, tender in a way that people like them aren't meant to be. And right here, right now, Zodi feels whole.