This was my entry for Ichiruki Big Bang 2017, hosted at .com (take out the spaces and parentheses!). You can see the art that my partner (jellyribbons on tumblr, if you wanna look her up) did on my blog, under my Collision Course tag!

Unfortunately, I wasn't able to finish the fic in the time limit, but I've written two chapters in full (thus meeting the 7000 word minimum quota), and the rest I will work on when time permits. I have a full outline in place, though, so hopefully it won't be too ridiculous of a wait between chapters. Please enjoy!

One

Gravitational Collapse

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There's a black mark on Ichigo's palm.

He's never spent too much time contemplating it. People attribute so many things to these tiny coloured markings that appear on their skin. They say it tells you the kind of person you are, the kind of person you're going to be. They say the person you're destined to be with — your soulmate — has the exact same mark somewhere on their body. Because that's what the definition of a soulmate is, isn't it— one soul, two halves, split between two separate forms. Alike in every respects. There are entire religions based around this concept, dating sites that cater exclusively to making sure you meet up with your other half. Psychics that claim they can read your entire future from that one mark alone.

Ichigo thinks, it's just a goddamn birthmark.

He hates all this destiny crap surrounding these marks. When Tatsuki had asked him at the age of thirteen what his mark looked like, he'd scowled and told her to shove off. His hand had clenched, reflexive, around the shape getting ever-clearer against his tanned skin. She'd harrumphed, unperturbed, and informed him hers was the shape of a crimson eagle and that it clearly meant she was destined for greater things than him, if his mark was still the misshapen blob she remembers it being when he was nine. He'd responded that her mark looks more like a puddle of spew than the eagle she claimed it to be, and she'd thrown a well-aimed kick at his shoulder and the conversation had been dropped.

By the time he's fifteen, the mark is well and truly etched onto his skin, no longer misshapen by any stretch of the imagination. Still, he refuses to pay too much attention to it, refuses to try to analyse the shape it's settled into. It's all bullshit, anyway. If he squints, he thinks you could almost mistake it for an ink-black sun — see? Bullshit. There was only one sun in his life, and she'd set six years ago and taken all the light in his family with her. His mother was the sun, the one holding them all together with her gravity; not him. And if his soulmate is anything like him, if they, too, are represented by a dark black sun mark somewhere on their body, then he wants nothing to do with them. He wants nothing to do with himself, most days.

So when Keigo asks, exuberant, innocent, what his mark is, Ichigo looks him straight in the eye and tells him he doesn't believe in destiny.

And he doesn't. Not even now, after she comes barreling into his life and gifts him a power he thought he'd never have; after she fits into the cracks and crevices in his life so seamlessly he forgets there were cracks there in the first place. She sleeps in his closet and steals his food and charms all his friends (and he has those, he notices all of a sudden; he has a lot more of those than he had last reckoned, when had they all got there—?), and Ichigo would like to say he's irritated, only he isn't. She's so different to him, and he can't seem to get a handle on her the way he has with other people in his life. But still, somehow— they're the same when it comes to the things that matter. He won't put that down to something as illusory as destiny, though, won't do their bond that disservice; what he has with Rukia is real, built on tangible things like shared grief and mutual irritation.

He catches a glimpse of her mark once, just once— soon after his fight with Grand Fisher. It's a windy day, and her uniform skirt rides high on her legs for a single instant. It's not like he was looking, he swears, but he doesn't have time to turn away before the flash of bare skin has him rooted to the spot, turning bright red. She notices, of course she does, and smooths her skirt down, aiming a sharp elbow into his ribs. He doubles over and pretends to have not seen the shape on her upper thigh, almost imperceptible against her paleness. A white crescent moon, a mark that couldn't have been more different to his own than night and day.

It's nothing he doesn't already know, and he tells himself the small twinge of emotion that goes through him at this revelation isn't disappointment at all.

"Of course shinigami are aware of the concept," she says brusquely when the subject comes up, after a long day of Keigo trying to wheedle the location and shape of her mark out of Rukia. It's considered— if not rude, then a little gauche to ask it of people, but that's never stopped Keigo before. She perches on his desk and swings her legs to and fro; her dress is getting rucked up around her thighs and Ichigo bites back a caustic remark. It's better than her sitting on his bed, at least. "We were all human once, too. We just don't put that much stock in it, is all."

This surprises him more than he cares to admit. "Why?" he asks, careful to keep his eyes trained on his homework lest he seem too interested.

She snorts. "We are soldiers, Ichigo. Love and partnership have no place in our lives. And besides, most of us have lived for hundreds of years, well beyond a single human lifespan, and have never managed to come across our so-called 'other halves'. If they truly do exist and I was destined to spend the rest of my life together with them, you'd think the universe might have made it a little easier to meet them, no?"

He sits up slowly. "That doesn't answer my question," he says, and he doesn't miss the way her shoulders tense up the tiniest bit. "I said, do you believe in all that soulmates crap associated with these marks?"

"Of course not, you fool," she snaps, but something in her eyes are telling him yes, yes. Her fist bunches in the fabric of her dress, which has ridden up high enough that he thinks he's almost going to see her mark again; but then she jumps off his desk in a fluid motion and her dress settles around her legs once more. She turns away from him and climbs into his closet. "Do you?"

She doesn't know he's seen her mark yet, but he knows she's seen his; it was one of the drawbacks of having it in a more obvious place. As much as Ichigo doesn't believe in the mythology surrounding these marks, a part of him is uncomfortable with the idea. It feels too much like wearing his heart on his sleeve to have it so visible, that people will see it and draw whatever conclusion they like about him through this insignificant blotch of pigment — not that his hair doesn't already have the same effect. He thinks of this, of the fact that she knows their marks don't match, and wonders whether she'll think of it too when she hears his response. Wonders why it should matter at all.

"No," he says, and his voice is firm. Behind the shut closet door, Rukia's silent.

"... Good," she replies after a while, and if Ichigo didn't know any better, he'd say her voice was wavery, almost like she was crying. "Silly, human superstition, that's all it is. Did you know you can fall in love with someone who doesn't bear your mark?"

He didn't, but staring at the closet door, fighting an odd urge to slam it open and demand if she was ok, Ichigo thinks he can understand how that might come to happen.

In hindsight, it's obvious that not all the couples he sees around him are mark-matched. Human beings are frustratingly contrary creatures, and even if the marks had been a surefire way of finding your romantic soulmate, he's sure some people (like him) would have said bollocks to that. Tatsuki's parents, for one, have slightly mismatched marks; Mrs. Arisawa's is a lime-green leaf, while Mr. Arisawa's is a viridian blade of grass. Still, Mrs. Arisawa laughs, casting her husband a fond smile, at least their marks were both plants; her sister with a flower mark had married a man with a pouncing tiger over his shoulder. They fought a fair bit, but despite everything, they were still together.

"And so are we," she declares, plying them all with tea and biscuits as they get on with the study session they'd opened for Rukia's benefit. "Don't mind the people who tell you mark-matched coupling is your ultimate goal in life. Romance isn't the be-all and end-all, and besides, it's perfectly possible to be wildly in love with someone who doesn't wear your mark at all."

"Mom, will you stop being gross? Nobody asked for your sweeping tale of romance with dad," Tatsuki grumbles, but a good half of their group is listening raptly, hanging onto Mrs. Arisawa's every word. Even Ishida, detached as he's trying to appear, is clearly not concentrating as hard on his maths as he would have them believe. Inoue, Keigo and Chad have outright dropped their pens. Only Mizuiro and Rukia seem unperturbed, although maybe that's the wrong word for Rukia, who is gripping her pencil so tight the tendons are standing out against her skin. Ichigo thinks it's time to steer the conversation into safer waters.

"Man, how the hell are you supposed to solve this question? Did we learn this?" he complains loudly, throwing his pen down. Several heads turn in his direction, and Ishida mocks him a little for not grasping such a simple concept; it's Inoue who bows her head over his worksheet and kindly points out the trick to the solution. He nods in gratitude and quickly fills the rest of the question out.

"I— it's nothing, Kurosaki-kun!" Inoue trills, flashing him a hesitant smile, and he pauses, a little taken aback; he smiles back cautiously, and watches, completely nonplussed, as her cheeks become suffused with red so that the six-petaled flower mark on her cheek becomes very noticeable. The thought pops into his head, unbidden, that he's sorry for her, to have her mark so prominently on display. But then again, it fits with the kind of person Inoue is; bright, loud, open in her affections for everybody. Flustered, she turns away from him, and once her head moves out of his line of sight he sees Rukia behind her, staring at him with a confused expression.

But you did that question just last night, he knows she's thinking, and it's true; he helped her with the very question he pretended not to know just then. He scowls, and hopes it'll be enough to throw her off the scent.

It is, but not in the way he hoped it would; Rukia inclines her head the tiniest fraction, as though she's thanking him for what he did, before turning back to her work. Ichigo's scowl deepens. He did nothing that was deserving of her thanks. It's not like he moved the conversation along for her; he doesn't like seeing her so obviously distressed, is all. She needs to be the annoying bitch that she is 95% of the time so he can cuss her out in his mind in peace.

He turns back to his own work, trying to drown out Mrs. Arisawa's words ringing in his ears.

It's perfectly possible to be wildly in love with someone who doesn't wear your mark at all.

He knew this already; a stupid fucking confirmation shouldn't change anything—

and yet.

When they come for her, it's when the moon in the sky resembles the moon on her thigh; a delicate sliver of a thing, barely visible against the inky darkness. Some cocky bastard with dark red hair that reminds Ichigo of old, bad blood and a cold one whose eyes give new meaning to the phrase if looks could kill show up to take Rukia to her execution, because, oh yeah, apparently lending her powers to a human being for any reason is a capital offence. Rukia, fucking Rukia, throw-herself-in-front-of-a-hollow-for-a-stranger Rukia, as-if-I-would-do-anything-to-make-you-worry-about-me Rukia, that Rukia, shuts down in their presence; goes cold and still and withdrawn like the glaciers he learned about in geography class. Something about that picture, her silent and sheet-white and scared against the backdrop of the pavement, strikes him as deeply, profoundly wrong; Rukia shouldn't be wearing an expression like that. Ever.

He takes up the sword that she has given him and thinks, finally, finally, he's going to be able to repay his debt to her, but before he can finish the red one off and get to the one with the cold, cold eyes, he falls.

At first he doesn't quite understand what's happened; his body spurts blood redder than the cocky bastard's hair and then there's the pain of it, belated, bringing him to his knees and further still. He collapses face-first onto the street, into a puddle of his own blood; Rukia screams aniki and the red one slams her into a telephone pole, by the neck. Ichigo struggles to rise, but his limbs won't heed him, and he's on the verge of losing consciousness when the cold one (aniki, he was her brother, he was Rukia's brother) steps in front of him and addresses Rukia for the first time.

"I see, Rukia. This boy… resembles him a great deal."

Ichigo's hand shoots out to grab the hem of the cold one's robes. "Who do I resemble? Don't talk about me like I'm already dead."

The cold one stills, warns him to remove his hand if he wants to keep it, but Ichigo won't let go, can't let go; every second he manages to keep him rooted there is another second Rukia stays by his side. And he will not cede her, not to someone who looks at her so coldly; he can take his aniki and shove it. Brother or not, Rukia deserves better than someone who makes her look so uneasy in her own skin—

She kicks him.

She kicks him, and his hand falls to the ground; the impact of her foot, tiny as it is, stings like a bitch. She's saying something, but Ichigo can't make his brain parse the meaning from her words. His mind is filled with static, rising and rising like the tides; her eyes have gone cold just like her brother's, and for the first time Ichigo thinks he can see the resemblance. But this is Rukia, Rukia; Rukia who shared his space and lived under his skin for the past three months. It can't end like this.

She turns her back to him, andIchigo feels panic close his throat; he yells at her to stop, to look at him properly, but she won't, she won't. And if the last memory he ever has of her are those warm eyes gone cold, he won't be able to stand it. Look at me, please.

She does, and he almost wishes she hadn't. The tears on her face, like a premonition of rain, and Ichigo remembers being nine and helpless; wet with someone else's blood and alive because of someone else's sacrifice. He wants to reach out for her, because surely this time, he'll be able to protect; but six years hasn't made an iota of difference and he can only watch as she saves him again with her words and her actions, stepping beyond the gate to somewhere he can't follow.

The last thing he sees before the paper doors slide shut punches all the air out of his lungs; a directive from the heavens as if to say this is not your concern. For a fleeting moment, the wind lifts the scarf from the cold one's collarbones; there, etched onto milk-white skin, is a familiar mark.

A crescent moon.

The first drops of rain hit the pavement, and Ichigo drops his head to the ground and screams.