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"What the hell is she doing?"
The scene in front of Aether was more shocking than aggravating, or at least he wanted to think that. Since arriving at Teyvat, his twin sister had gotten bolder with each new region they traveled through. She'd always been the more introverted of the two; on other worlds, she rarely sought out interactions with people outside of her brother. If she did, it was because Aether was enjoying himself.
Now, he watched as Lumine and that obnoxious brat of a puppet made out against the wall. When had his precious little sister gotten so out of line?
Aether blinked, trying to come back to himself. What was he getting worked up for? Lumine was his twin sister, all he'd ever wanted was for her to be happy — to enjoy herself on their travels, to have new experiences. Not all of those new experiences had to be with him. In theory.
They were always and would always be two halves of the same whole. Lumine was his mirror, his other half. If he were akin to the sun, she would be the moon and the stars. He was warm, sociable, always looking ahead. His sister preferred quiet solitude and reflection. Getting to see emotions he didn't often experience in her face was almost as if he were looking at a what-if of himself.
Maybe that was why he didn't like watching his twin holding someone else, someone he didn't want. Maybe that was why his chest burned with an anger he hadn't felt in many years, a discomfort settling in under his skin.
He scowled. This was stupid, really. They might share a soul as twins, but Aether knew Lumine was her own person. She was allowed to do the things she wanted.
Aether turned away from the scene, deciding to leave without saying a word. Lumine had told him to meet her around the back of the inn they were staying after breakfast, but it seemed like she was too predisposed to remember.
Even as he stalked off, his scowl grew.
When they were younger — Aether doesn't even remember how long ago, now — he decided to grow his hair out.
His sister always preferred her own to be short. It would get in the way of fighting, she said with a shrug when he asked her about it. She kept two strands in front longer to frame her face, but always asked him to chop it off if it ever started to go past her neck. He used to keep his own in the same manner.
Their hair was both the same shade, a pale blonde that reminded him of hay. Their eyes, too, were the same honey color. In appearance, they were similar in every respect. Perfect copies of the other.
In life, they were complimentary. Aether preferred darker, warmer colors — his favorite weather, no matter where they were, was the warmth that crept in on early mornings. Lumine was the opposite; preferring cool tones and whites that reminded her of the snow that she loved so much. They'd both learned how to fight with a sword, but they moved as one instead of two. No attack could get past them when they fought together.
So he decided to grow out his hair.
Lumine had been taken aback, at first, when he'd declined her chopping it down for him like she usually did. "You don't want it cut?" She'd asked, doubt dripping into her words.
Aether had just smiled at her. There were a million ways they were the same. Maybe, if there was one in which they were different, he would have an easier time grappling with the way his feelings had slowly been changing over time.
"I think it'll suit me," he'd said with a shrug.
Lumine had frowned deeply. "But we won't… be the same, anymore," she'd said quietly, searching his expression for an explanation.
There wasn't one that he could've given her that would've made sense. "We're always the same," he'd told her instead. "Where it matters."
He'd never asked her to cut his hair down again, after that.
Aether and Lumine. Lumine and Aether. It had always been, and would always be, the two of them. Thinking that some random puppet of a person would get in between that was ridiculous. Even when they'd met others, even when they'd formed bonds and friendships, it had always been them, together.
The walk back up to their room at the inn was spent lost in that thought, that even if they were separate people — even if Aether had forced them to be separate people, because of a festering desire he refused to acknowledge — there wasn't supposed to be space for someone else. Aether wasn't ready to make space for someone else. Lumine was his. His twin, his other half, part of his soul. That wasn't for anyone else to take. She wasn't for anyone else to take.
Maybe they'd been in Teyvat for too long, he thought, if she was getting comfortable enough with someone to leave him—
"You're still in bed?"
At the entrance to their room at the inn, Lumine stood, looking—
Aether looked away. "Well," he said icily, "you didn't seem to notice when I came down when you told me to."
It was rare that they ever fought. They were too close for something as petty and trivial as little squabbles, and they both preferred long-form conversations over arguing regardless. He could count the number of times they'd actually fought in the traditional sense on one hand. Normally, there was no reason to get mad at the other.
The door creaked behind Lumine as she entered their room. "Oh," she said, somewhat lamely. "You saw that?"
There was something off about the way that she asked that, but Aether barely registered it. Instead, he studied her from the corner of his eye. She leaned against the now-closed door, looking at her shoes with her arms hugging herself loosely.
Composed. Casual. For some reason, that pissed him off even more.
"Hard not to," Aether said, finally turning to face her fully. He took a deep breath. What he needed, he thought, was not to be angry. He needed to get a damn grip.
A beat passed before Lumine spoke again. "Well, are you ready to head out? It's getting a bit late for us."
That was objectively untrue. They'd absolutely spent days doing nothing before, because where they were wasn't the important part — it was being together. The same anger bubbled up in his chest once again, threatening to burst. Aether generally had no trouble understanding Lumine, her moods, what she wanted or needed.
Now it felt like he was looking at a stranger. Everything seemed off, from the casual tone she was using to the way her smile didn't meet her eyes. When had she ever been so cold with him before?
"No," Aether found himself saying.
Lumine finally looked up. "No?"
They may have worn the same face, but right then, their expressions were practically opposites. Aether didn't reply, instead moving off the bed to stand in front of her, crowding her against the wall. His sister just blinked at him, unsure.
"Aether..?" Her eyebrows furrowed together, and for the first time that day she looked and sounded like the sister he remembered. It was almost enough to bring him back to himself.
Almost, but not quite. A gloved hand came up, holding Lumine's chin between his thumb and index finger. For a moment, she seemed to relax — casual touches between them were as familiar as breathing.
Nobody else should get to have her, he realized with a start. She was his. His twin, his other half, his to roam the galaxy with and his to hold and caress as he pleased. There wasn't any room for anyone else in his heart, and there shouldn't be any room for anyone else in hers, either. The image of Lumine being touched by hands that weren't his wouldn't seem to get out of his mind. Everywhere his eyes flicked to, he could see a phantom image, holding her in ways he never had. Kissing her like he never had.
As if struck by a moment of clarity, Aether nodded to himself. How long had he denied himself of what he really wanted? How long had he stayed convinced that they could go on forever the way they had been? It was foolish to think it, and it was even more foolish to not throw caution to the wind and not trust that his twin wouldn't meet him halfway no matter where he went.
If she wanted to be kissed, Aether thought, he would do that for her. If she wanted to be touched, if she wanted to be fucked — he could do that, too. Nobody knew her better than he did. How could anyone else please her as he could?
He jerked her chin up, forcing her to look at him again. "This is for your own good." Without another moment of hesitation, Aether closed his eyes and kissed her.
The first thought he had was that Lumine tasted like that honey tea she liked to have with breakfast. The second thought was not important, he realized, as he shoved his sister against the wall. He kissed her fiercely, the way that he'd seen Scaramouche do earlier, his teeth nipping at her lips. His hand that had been on her chin now cupped the back of her neck, angling her just so, while his other was pressed firmly against the wall to keep his balance.
It was dizzying, to finally kiss her like this. It was more dizzying to realize Lumine had wrapped her arms around his neck, pulling him in closer as she moved her mouth against his. Maybe he was imagining it. It didn't matter — the only thing that did was right in front of him.
He let his tongue trace her lips until she parted them just enough to slip inside. She moaned when he licked fully into her mouth, learning if the inside of her was the same mirror to him as the outside.
They fit together perfectly, really. Nearly the same size, it was easy to slot a leg between her own, pushing them out of the way so she could grind down onto his thigh if she wanted. When she pushed against him to seek that friction, he took advantage, breaking the kiss to bite into her neck.
He absolutely never wanted to see someone hanging off of his baby sister like that again. Absolutely never wanted to even think about it. So to be safe, he told himself as he sucked a bruise right onto her pulse point, everyone needed to know she was off limits. That they were each other's. Without one, there was not the other — in all things. A small moan escaped her as his teeth grazed over the now-sensitive skin, and he decided he wanted to hear more of that. He knew what Lumine sounded like in all situations — but not this. He'd never seen her like this before.
Lumine's arms came down to hug him tightly, fists tightening where his shoulders were and bunching his shirt together awkwardly. All the while, Aether had taken one hand to jerkily move her on his leg, trying to keep her overwhelmed from all angles. She was never allowed to think about someone else like this, now that he'd had a taste.
Aether pulled back for a moment to study her. The flush on her cheeks, the redness of her lips, the way her chest moved as she greedily took in air. The honey-colored eyes they shared reflected his own ruffled appearance back at him with how wide her eyes were blown out. Any doubts that remained fell away the longer they stared at each other. He should've been doing this forever. She was clearly enjoying herself, maybe a little too much. With a shallow breath, he filed that thought away for later.
Without waiting for her to come back down, he pulled Lumine off the wall and threw her somewhat carelessly down onto the bed. Before she could even open her mouth he was on top of her, then, kissing her with a passion he didn't know he had. His arms caged her in underneath him, and she wrapped her own around him to pull him down onto her more, fingers pushing their way into his long hair.
Almost timidly this time, Lumine rolled her hips against his. Aether broke the kiss to nip at her neck, wanting to hide the way he hissed at the tiniest bit of friction. He'd never — they'd never—
A shuddering breath, and he decided to take the lead back. He grinded into her, kissing the spot he'd bruised a few moments ago. He'd never done anything like this, but he knew. He knew what he was looking for, knew what would make her feel good, too.
They were the same. Of course he knew. What he wanted, she wanted, as it was always supposed to be. He was her big brother for a reason. The firstborn twin, the one meant to protect her, to hold her, to guide her. He sought out that delicious friction again, her dress bunched up towards her waist. Even through his pants, he could tell the panties she wore were already damp.
Good, he thought with a viciousness he didn't know he had. He didn't want anyone else to make her feel like this, to make her body react. Only him — only he could know her body inside and out, because they shared one. How could anyone else ever hope to please her?
"Aether," Lumine whispered, fervent as her breath scorched everything around him until there was only her, "don't you want— won't you—"
She, too, was not used to this. The more Aether moved against her, the more noises she made. A symphony of whimpers and broken moans, his name peppered in through all of them. He'd always loved the way her voice made his name sound.
Aether, the clear sky, above the clouds. He was nothing special without Lumine, who could shine and illuminate him.
He sat up, kneeling on the bed with her in between his legs still. The shirt came off easily, braid messily getting pushed around by the motion. Her dress was next, sliding over her head with a little difficulty. He still had his pants on, but that could wait. He wanted to hear what else Lumine could sound like, first.
Her bra came off next, dropping it in the pile on the floor without a care. They'd seen each other naked before, of course. They still bathed together when they were feeling unwell, dressed each other when too tired. Never had Aether taken the time to stare at the pink of her nipples, the way her breasts fit in the palm of his hand perfectly.
"Beautiful," he said absentmindedly, letting a thumb drag across her nipple. Underneath him, she shivered, moving her legs against each other trying to recreate the friction of a few moments ago.
He paid her struggles no mind, choosing instead to focus his efforts on learning the ins and outs of the body parts they didn't share. He pinched her nipple lightly in between his thumb and index finger, rolling it when she hissed in pleasure.
That was a nice reaction, he registered somewhere in the back of his mind. He did it again, this time with the other nipple. Lumine continued to writhe underneath him, drawing his attention to the fact that he was starting to grow painfully hard himself. His pants had been feeling tight since he'd shoved his twin against the wall, but there was no reason for them to still be on.
Pushing himself off the bed for just long enough to kick off his pants, an idea struck him.
In the state she was in, she wouldn't say no. Not that Lumine would say no to him normally anyway — what he wanted, she wanted, and vice versa. The idea took shape in his mind, morphing from a passing thought to a carnal desire he hadn't known he possessed.
Looking at her, though, spread on the bed with only her panties still on and breathing hard, Aether knew he had no chance of stopping himself once he was inside her.
"Aether," she said, a touch whiny. "I— I want—"
He crawled back over her, smiling gently. "I'll take care of you," he promised, meaning every word.
There was no point in removing her underwear. He pushed them to the side, letting a finger slide against her. He hadn't known how wet she was, but was grateful for it nonetheless. It made the push inside of her to tease her a bit much easier, even as his cock hang heavy and hot with his own desire.
They'd touched themselves, of course. It was one of the few activities they tended to do in private, either while in the shower or alone in a bed while the other got food together or did some early morning exploring. Experimenting with one's own body, especially when one had the long lives they did, was normal. Natural.
He'd never seen her do it, but he'd seen videos. They were popular on most planets they ended up on. Watched the anatomy he didn't have, watched fingers glide in and out, watched fingers circle around a clit. Despite not knowing why, he'd paid a bit of attention. Couldn't remember what the girls in the videos looked like, couldn't remember what they sounded like, but he could remember pretending it was Lumine he was watching instead.
So Aether mimicked the motions he'd seen — one finger quickly became two inside of her, and he watched completely enraptured as they disappeared inside of her for a moment. If he pressed upwards, the pads of his fingers could feel her walls, could feel the way she spasmed underneath him, pressing both her hands over her mouth to keep herself quiet. She was so warm, so tight around his fingers.
"My sister is so cute," he said to himself, moving his thumb to push more of her underwear to the side so he could rub her clit for the first time.
Lumine practically jumped, back arching when he pressed into that sensitive spot. It was nice to see her like this — she was normally more reserved than he was, less expressive to the average person. Watching her squeeze her eyes shut, hearing her muffled moans…
That was taking too long. Aether pulled his fingers out from her, pumping himself for a moment. Though he didn't need to in the slightest. He was harder than he could ever remember being before, all at the thought of getting to fuck his baby sister.
Her underwear could stay on, Aether decided. They were cute, dainty things — black with some cute lace detailing, probably bought at one of the many markets in Teyvat that they'd been to. He liked them.
Pushing them out of the way, he lined his cock up with her opening, watching Lumine carefully. He wasn't sure what he was searching for in her face, but he committed the expression to memory regardless.
Then he finally, finally moved his hips and pushed himself all the way inside.
The effect was immediate. He almost fell on top of her, completely overcome by how fucking good it felt, how warm and wet she was as her walls clamped down on him tightly, almost trying to make sure he stayed. Lumine keened, hands flying from her mouth to dig her nails painfully into his arms.
He pulled out slowly, mesmerized by the way her eyes wouldn't leave him even then. Just as it should be.
"Only me," he told her, voice thick with want. "Only me."
She nodded frantically, legs coming up to wrap around his waist. They groaned simultaneously at the slightly different angle, letting Aether go in even deeper. "Only you," she agreed without reservation. "Please, please, I want you to—"
Well, if she wanted it so bad. Who was he to deny his precious twin anything?
This time when he pushed into her, he did it with as much strength as he had. He felt a little boneless, still, at the sensation of being inside of Lumine, but no matter. Lumine cried out, legs quivering around him.
The friction, he found, was the best thing he'd ever experienced. As he moved in and out of her, the way her cunt clenched down and he could feel everything was almost unbearable. He wanted this every day. He wanted this all the time.
Neither of them were going to last. As Aether's hips sped up, Lumine's fingernails scratched into his back, raking themselves down as she struggled to keep composure.
"Go on, Lumi," he breathed into her ear. "Show me how good your brother makes you feel."
She tightened around him as he kept fucking her, slamming her eyes shut as she came. Beautiful. She was so, so beautiful in that moment, crying out his name as he brought her to the peak and let her burst.
A tightness was growing more pronounced in his abdomen as well. He wasn't far behind — there was no way he could last much longer when she felt like that when she came. He let his head fall onto the side of hers, mouthing at her shoulder. His movements became more and more frantic and erratic as he chased after his own release.
"Aether," she said, voice hoarse. "Not— not inside please— we can't—"
Aether hissed, having the wherewithal to push himself up and bring one hand down to her hip to hold her in place. Lumine screamed as he spilled into her, making sure he pushed his cock as deep in as he could. His own eyes closed as his mind went completely and blissfully blank, rocking into his sister with stuttered movements.
He collapsed on top of her moments later, bringing his hand up to pet her hair even as he smothered her.
"Why did you— Aether—" Her voice was strained, and he couldn't place the emotion in her voice at the moment. That was fine, he decided. He'd dissect it later.
He maneuvered them just enough to be more on their sides, cock still inside of her, and kissed her gently on her soft, swollen lips. "Shh," he whispered, smiling at her in the most comforting way he could. "I'm sorry. It was an accident," he lied through his teeth.
Lumine's eyes glistened. "An… accident?"
He'd always been the better liar out of the two of them. His smile grew before he kissed her again. "An accident," he repeated. "Now sleep, I'm sure you're tired too." He closed his eyes, pulling her tightly against him. Inside of her still, his cock twitched.
Her breath hitched, even as she slowly moved to hold him back. "Okay," she agreed, a shuddering sigh leaving her lips with it.
Aether didn't notice, almost, until the next morning when sunlight peaked through the blinds.
Lumine hadn't once told him to pull out, even as they'd gone for round two and then three. He'd come inside her both times, and she'd protested, but she hadn't told him to stop. Hadn't told him not to fuck her again. Hadn't even bothered to ask him to pull out of her so she could clean up a little in between sessions and sleep.
Smiling into her hair, he closed his eyes once more, ignoring the rising sun. As always, it seemed, he and his twin were truly mirrors of each other in all the ways that mattered.
Maybe he should cut his hair.