A/N: I said I'd write a Rivetra bodyswap fic months ago and here it is (come on, every fandom needs one).

The summer night is oddly cool, warm instead of hot and dry instead of sticky, and when Levi steps outside for a moment to breathe in the fresh air, he finds himself lingering.

Above his head stretches the night sky, an infinite expanse of deep blue glittering with stars, and he tilts his head back to search for the constellations he still has memorized. He's been looking for them since he was a child, through the curtains on his windows, in the still darkness of night with blood on his hands, on the rooftops of Sina with the wind in his hair and the idea of freedom hidden somewhere in his heart. Finding patterns in the stars calms him down, helps him think, and after a few minutes the numbers and letters swirling in his mind start to cease.

It's something he should be used to by now, returning after every expedition, filing reports and scrawling signatures and recording statistics like every word, every name he writes was not once flesh and blood, full of life and hope, and every time he comes back and sits down in his office to do the necessary paperwork, he always feels selfishly glad the people he cares about are never among the names he documents. But sometimes he recognizes some of the names, can recall a face to match the letters, a smile, a pair of eyes or hands or a brave voice, and after too many such cases he needs to take a break.

He is contemplating the sky, wondering if it is infinite or if it might stop somewhere far, far beyond the walls, when the door opens behind him.

"Captain!" It's Petra, still wearing her uniform jacket and pants; she comes outside to stand by him. "Long day?"

"You could say that."

She makes a quiet noise of agreement and he glances at her out of the corner of his eye; she hasn't changed after dinner but her feet are in a pair of slippers and her shirt is buttoned crookedly. He slants his eyes forward again and finds himself wondering out of the blue exactly how old she is.

"The weather's nice today," she says. "It doesn't feel like summer right now."

"Hm."

"And the stars are so clear tonight." She smiles, points up at a particularly bright one, flexing her wrist. "Have you ever made a wish on a star before?"

"No."

"A dandelion?"

"No."

"Birthday candles?"

From what cake, he is tempted to say, but holds his tongue and simply responds, "No."

She peers at him curiously. "Have you ever made a wish before?"

"There's no point."

"Surely you must wish for something."

He stares hard at her, at the small smile playing at the corners of her lips and the sharp way she is looking at him, and he thinks about all the past times they've done this: speaking in riddles and half-hints and almost-questions, pretending they don't find each other on purpose, always bumping into each other accidentally when no one else is around, glancing too directly and lingering too long and standing too close.

I wish I knew what game you're trying to play. I wish I didn't have to worry about this squad's safety every expedition. I wish I didn't have to be captain for just one fucking day, he thinks, but in the end he only shrugs.

"I see," Petra says, and he doesn't look at her now but he thinks her lips must be pursed, her expression thoughtful, maybe a little bit disappointed.

"I'm going to go to bed, captain," she says after a pause. "Good night."

He nods and does not watch her go, choosing to stay outside among the stars, and when he turns his eyes back to the sky he could swear one of them winks at him.

When he wakes up the next morning, he doesn't have to open his eyes to know something is wrong.

For one thing, there is far too much sunlight beyond his shut eyelids—he likes to get up when the moon is still out, when the sun is just a hint of color on the horizon, but there is too much warmth on his face and he knows when he finally opens his eyes he will have to squint and blink multiple times until they adjust to the bright glare.

For another thing, his body feels strange—oddly light, as if his muscles have shrunk overnight, but it is not like they have loosened; he feels the energy thrumming through his body like it usually does after a good night's sleep, but he doesn't recall sleeping particularly early last night and oversleeping usually makes him feel groggy.

Then there is the fact that the bedsheets do not feel like his own, not to mention that there is hair tickling the back of his neck, and considering how long the hair is on the back of his head, the sensation confuses him.

Somewhere deep in the pit of his stomach he knows he won't like what he sees when he opens his eyes, but he can't lie around all day so he might as well get it over with.

It only takes a quick look at the ceiling to confirm his suspicions.

This isn't his room—there are chips in the paint, little blemishes that he dealt with in his own room the day it was assigned to him. He sits up slowly, rubs his eyes, looks around, and takes a deep breath.

The bedroom is not as large as his own, and not nearly as well kept. Clothes lie in a heap on a chair in the corner, books are stacked on the desk against the wall, and the closet door is open, revealing a haphazard arrangement of items not hung by color or article. Something catches his eye and he freezes for a moment when he recognizes the brush lying against the mirror on the vanity; a silver-handled thing with strands of orange hair caught in it that he can see all the way from the bed.

He remembers Petra running it through her short bangs once, trying to smooth them out, and he racks his mind for a clear memory of the night before.

He went inside shortly after Petra did, took a bath and went to bed—it is all he can recollect. He did not run into her again in the hallway, outside his room, and he most definitely did not have anything to drink that might blur his memories; he is perfectly aware of his own lack of tolerance for alcohol and he would have a pounding headache right now had he been drinking the night before.

Maybe he's not in Petra's room then—though wherever he is, it's definitely not his own room, and he should be questioning how on earth he got here anyway.

He looks at the brush on the dressing table and decides to go check; there was a scratch on the side of the handle last time he saw it and he knows for sure because he was watching her brush her hair, noting the little scars on her knuckles and taking in the mark on her hairbrush as well. He pushes the bedcovers back and stands, making his way across the room.

Even his balance is off; his chest feels oddly heavy and he usually doesn't move his hips this much when he walks. He frowns, reaching the vanity in a few strides and picking up the brush, turning it over in his hand to look for the scratch—turning it over in his hand, his pale, slender hand that does not look like his own.

He closes his eyes again and counts to ten, telling himself there is nothing to be alarmed about. With his other hand, he reaches for his jaw—and brushes locks of hair right next to it.

There is nothing to be alarmed about, he repeats to himself, over and over, and then he opens his eyes and looks into the mirror.

Part of him already knew, but the brush drops from his hand anyway, and when he lets out a strangled curse, he has to acknowledge that the voice is exactly what he thought it would be.

Petra wakes up feeling strangely heavy.

She slept early the night before, trying to put certain people out of her mind, and she expected to get up early as well, rise before the sun and head downstairs to start boiling a pot of coffee like she does nearly every morning. It's tiring sometimes, being around her captain, and in these times she likes to sink into habit, feeling safe in the comfortable pattern of routine.

But already she can tell her day is off to a bad start; the sun's rays are much too strong, which means she overslept. Yet sleep usually does her good; her eyes feel lidded with exhaustion, her limbs cumbersome, little creaks of pain wedged into her spine, and she groans as she sits up, swiping a hand over her eyes and stumbling out of bed to grab a pair of pants to change into.

It takes her another few seconds to open her eyes fully, and when they do she halts.

This isn't her room—she doesn't have such a huge desk opposite her bed, stacked with tall piles of neatly stacked folders; nor are her floors spotless, the top of her drawers bare, a notable lack of personal items adorning the shelves in the corner. This room looks barren, hardly lived in, but it is bigger than hers and there is something very official about the sealed envelope on one side of the desk that makes her think this room belongs to a ranked soldier, someone like a squad leader or even the commander or—

Right. The spotless floors should have given it away instantly.

There is no reason for her to be in Levi's room; she's seen the inside once before, a few months ago when she was delivering reports, but that was a brief flash through the crack in the door and of course there was no reason for her to enter. She glances around the room, but it's not that big and she is most definitely the only one here.

So then what is she doing, alone in the captain's bedroom?

Besides the door that opens into the hallway, there is a closed door on the far side of the room, which must lead to a bathroom of some sort. Perhaps he is inside; she can demand answers from him.

As she walks she can't help feeling decidedly odd; her arms usually swing lightly by her sides but there seems to be an extra bit of weight there today, and the way she usually walks now feels unnatural, uncomfortable, but she can't figure out why.

She wonders how she got here in the first place—she's never sleepwalked before, but she supposes the possibility can't be ruled out. Could he have brought her here? But no, he wouldn't do that—she knows he isn't that sort of man, and if he were she wouldn't want him anyway.

The door in the corner of the room pushes open easily, and she enters to find it is indeed a bathroom. She turns, and nearly runs straight into Levi.

He isn't wearing a shirt, and she tries not to stare, but she can't help taking a quick look anyway. He stares at her too, and when they look each other in the eyes she thinks their expressions must be exactly the same—confused, a little embarrassed.

"What am I doing here?" she wants to know, cutting straight to the chase, but he speaks at the same time she does and his voice overpowers hers. She frowns and he does too, as if he were the one who woke up in a bed that was not his own with no recollection of how he got there.

"It's your room," she points out, folding her arms across her chest—and suddenly gulps, because he does the same thing at the same time, but she feels skin and not the fabric of her shirt against her arms, and the skin is smooth. Flat.

An idea comes to mind, but she rejects it instantly because it is improbable—no, impossible—and she can't take it seriously. Still, she checks, slowly reaching up to touch her hair, and her fingers brush thick short locks briefly before they find the back of her head, smooth and shaved.

Levi copies her motions exactly, and now she's nearly positive, but no, it can't be, so she moves forward to touch his face as he does the same—

Her fingers only meet glass.

Petra closes her eyes, counts to ten, then opens them again and screams.

Levi's hardly had time to think, to wrap his mind around just what the fuck happened to him overnight, and before he can start to freak out too much, a thought occurs to him.

If he's here, in Petra's body, then Petra must be…

He's nearly at his own room when he hears a hoarse shout sound from inside.

Instantly he throws open the door and rushes in; no one is there, but the door to the bathroom is ajar. He approaches cautiously, knowing what he'll find, yet when he turns the corner to see himself gripping the edge of the sink and breathing heavily, it still comes as a rather nasty shock.

"… Petra?" he says slowly.

She—he—his body—whips around to stare at him, and when they lock eyes he has a sudden intense desire to laugh, because he's sure even on the rare occasions he loses his composure, he doesn't look that panicked. The eyes are his, blue-gray and cold, but the sheer emotions—in this case, confusion and fright—are utterly Petra's.

"Levi?" she—he—his voice—fucking hell, this is weird—whispers.

"Yeah," he says dryly. "Any idea how the fuck this shit happened?"

And of course, it's strange to speak because the voice that comes out now is sweet and feminine and most definitely not his. He's heard Petra swear before, just a few times, but her mouth is nowhere near as foul as his and judging from the expression that crosses her (his, he thinks, but he decides to stop that line of thought before it gets too confusing) face, listening to her own voice say such things is… interesting, to say the least.

"No idea," she finally says, taking another deep breath and letting it out slowly, clenching her hands into fists and digging her nails into her palms. "I just woke up and… was here."

"Same." He looks around the bathroom, glances at the two of them in the mirror—he's never seen Petra's face so, well, dark before, completely lacking in its usual good cheer, and he's certainly never seen himself look so ready to throw up.

"This… doesn't happen," Petra says, shaking her head like denying the situation will make it reverse itself. "Ever."

"Making history, I guess," he says dryly.

"This is the strangest thing ever—"

"No shit."

"I have a dick."

He cocks his head at her and she refuses to meet his eyes, a tinge of red creeping up her cheeks. Odd, he's never seen himself blush before. "And I have breasts," he says.

The red spreads across her face. "Don't touch them if you don't have to."

"Wouldn't dream of it."

She sighs, shoving her face in her palms for a moment before looking up again. "I've never heard of anything like this happening before, except maybe in old stories, but those are just fairy tales and things like magic wands and poison apples and three wishes don't exist."

He would agree with her, but his brain catches on two of her words, and with a sudden sinking feeling he remembers a detail of the night before very clearly. "Petra."

She jerks her head to look at him immediately, and her—his—whatever—eyes are wide, bloodshot, almost wild. "What?"

"Last night. When you said I surely must wish for something."

She blinks once, twice, then slowly, a smile starts to creep over her face—and since it's actually his face, he finds the effect rather creepy. Maybe he is right to never attempt to smile. "Did you wish on a star, Levi?"

Even though it's his own voice, hearing her call him by name is a first he takes note of, though now is hardly the time to think about ranks and titles. "Suppose I did," he says. "Wished I didn't have to be captain for one day."

"And now you're not," she says, eyes closing, shoulders sagging, as if everything has been made clear, a burden placed upon her. "I am."

There isn't time, he realizes, to talk through the technicalities of his so-called wish; he wants to sit down and try to piece together how exactly the fuck any of this is possible, but it's well past sunrise and today isn't a day off; the rest of the squad should be downstairs, expecting them, and there is no chance in hell he's going to tell anyone—least of all Erwin—what transpired.

"One day," he says. "Just one day. Can you pretend to be me for one day?"

Petra's eyes snap to his. "What? You want me to be you for one day?"

"Well, you already are," he points out. "And you're good at things. You're a good soldier. A good fighter. You can probably be a good actress… actor… too."

"Thanks, but it's not the same."

"Well, you know how I act, don't you?"

He doesn't mean the words in any particular way, just as an offhand comment, but she bites her lip and he suddenly wonders how much attention she pays to him when he isn't looking, if it's anywhere near the amount of attention he unwittingly gives her.

"Yeah, I guess I do. But then you'd have to be me."

"I'll try to smile," he promises, and he is being perfectly serious but she snorts.

"I can try," she says slowly, "but… well. Is it necessary? You don't think telling anyone is a good idea?"

"No," he says immediately. "If tomorrow it's like this… perhaps. But it should just be one day."

"One day." She nods. "Right. Should be okay."

"We should go downstairs soon. It's late."

"Yeah."

"You should dress," he advises her, and it's technically his body that's half-naked but she blushes anyway.

"Uh, one thing," she says, avoiding his eyes, tapping her fingers awkwardly on the sink counter behind her.

"What?"

"I kind of really have to use the bathroom."

Levi closes his eyes and counts to ten again not for the first time that morning. One day. It's just one day.

A/N: I'll probably continue this someday if anyone's interested/the inspiration hits. Also I'd like to credit Advocaat for this fic; I read her brilliant Zutara bodyswap ages ago and will inevitably use some elements of that in here.