Author's Note: I always crosspost late, so: happy belated Valentine's Day! This is said holiday, adapted to Westeros, and is therefore about what you can expect when you mix the twins and a lovers's celebration.

Greenstone, Jaime thinks, doesn't really have much to show the world – it's a miserable little island with its miserable, not so little castle, and its miserable little occupants – but it does consist mainly of stone and greenery, and that has got to be a good thing. This way, when he and Cersei slip out of its long, cold hallways and into the warmth of the night outside, no one can hear a word of what they say to each other – it's all drowned in the noise of the waves relentlessly lapping at the rocks and the muffling effect that the thick ivy that crawls up the towers provides.

With that in mind, he doesn't particularly hesitate when he corners Cersei in her temporary chambers for a kiss, and hesitates even less to escalate it when she responds. On the entire trip from King's Landing to this gods-forsaken corner of the Stormlands, she'd played some bizarre game that had meant that he could do anything but touch her – he could watch her pleasure herself or let her suck his cock or anything else of the sort, but she'd stopped whenever he'd actually reached for her. He hadn't minded terribly – Cersei sucks him off as if her life depends on it – but over time, the frustration of not being with her properly had started piling up, and he'd understood the point of her little experiment. Even her one-sided attention is heavenly, but he wants more and she'd pushed that desire to the boiling point. He's so desperate for it that he falls to his knees before her, pushing her skirts up as soon as he realises that she'll allow it this time, and his mouth is on her before she can say a word more.

"Oh, yes, Jaime." His sister is leaning on the windowsill behind her and he draws one of her legs forward so that it rests on his shoulder; nudges the tip of his nose against her clit before opening his mouth fully, pushing his tongue right into her without as much as a warning. Cersei moans and then laughs, breathless and a little embarrassed, just as he'd known she would be. His cock twitches, as eager for attention as she is, but he can wait, Jaime thinks – having her is a much better reward than his own hand is. She's devastatingly beautiful today, dressed in a gown so low cut that bending forward seems to be entirely out of the question, and it's held together by a ribbon at her waist – one pull and it'll be gone. They can't, though, he knows; sooner rather than later, they'll be summoned down to meet their hosts at last, and they have to be quick.

Still, "I can't wait until tonight," Jaime murmurs against her burning skin, pressing a heated kiss where his tongue had just been, smiling when it earns him a gasp in return. "What was it today? Some fertility festival?"

"Day of the Mother Above," Cersei clarifies, and the words come out rushed, her hand in his hair flexing reflexively as he slowly works his tongue inside her again. "But yes, a fertility festival, too. Here in the south, they believe that if a bride wed within the last year— yes, Jaime, please, just there." He thumbs at her clit to get her there faster and her thighs clench around his head, but she continues valiantly. "— if a union is consummated when the Day of the Mother Above falls on the full moon, it's known to bring prosperity and— and abundance to her land— oh, brother, yes."

Every bit of this is familiar – the way she chases after his touch, the building urgency, the small noises she makes in the back of her throat – and Jaime knows just when to pull away to leave her wanting.

Cersei's face is a study in disbelief before it dawns upon her that this is a form of revenge, and then she sounds almost comically distraught. "Jaime—"

"Jaime," he parrots back at her, though the teasing is somewhat bellied by the fact that he wants her as much as she wants him. "From what I'm hearing, we have a union to consummate."

His sister's startled expression makes way for something far more wicked. "Lie down, Jaime."

She stalks towards him until he does, falling onto his back on the plush mattress, and then climbs up with him, straddling his thighs. He drinks in her every movement and groans when she slaps his hand away once he makes to unlace his miserably tight breeches; watches her, enthralled, as she gathers her skirts out of the way once again and plunges her own fingers inside her waiting body, whimpering at the sudden intrusion. Jaime is well-familiar with jealousy when it comes to his sister – she's married to a king, after all – but had never expected to want to upstage her very own hand. It's not a particular surprise that she'd thought of it. Cersei is nothing if not proficient in cruel, unusual punishments. She moans again, that brief, breathless sound that he loves to coax out of her, and hurries her pace along just a little.

In the end, the only thing she allows him to do is hold her by the hips as she brings herself to a climax on her fingers and his clothed cock, and Jaime feels distinctly more tortured than before by the time she gets up and tosses a towel in the bed's general direction.

"You look a mess, brother." There's a becoming flush to her cheeks and a thin sheen of sweat giving her an additional bit of glimmer wherever her skin is visible – so, quite a lot of it, at present – but she's enviably well put together, given her circumstances. "We'll be meeting the Estermonts soon; you better be presentable by then."

And with that, she leaves him behind, the door falling shut behind her with a decisive click.

Turnabout is fair play, Jaime has to concede, but he's awfully good at escalating things, as they both well know, and his plan to one-up her starts to form as soon as she's gone.

Knowing Cersei, that's precisely what she'd been hoping for.

~.~

The day had been long and terribly boring and he had almost become a kingslayer yet again, and Jaime is beyond grateful to be done with it as he and Cersei find themselves on the tiny strip of sand and rocks at the very base of Greenstone, his sister already tearing through his clothes between furious, starving kisses.

"We have to be careful," she says, because of course she does – even in her anger, her first thought is their survival.

He's not thinking about survival, though. He's thinking about her whispered descriptions of how today's festival is supposed to be celebrated, and the thinks she'll let him do. He's thinking about what she'll look like when he finally has her in his arms after all those long, long days of travel. He wants to erase every wretched memory of her worthless husband out of her head. "I don't want to be careful."

"Jaime," she complains, as she always does, but seats herself on a small gathering of mossy rocks when he pushes her towards them. He sinks between her legs for the second time today and his sister pushes her gown this way and that to give him access, almost as if she doesn't have to think about it at all – their union, once again, is a fact of life as much as her caution is. "If someone sees—"

"Be quiet." That's the last thing he wants from her, of course, and Jaime presses two fingers inside her as a further challenge. She's soaking wet already and it makes his mouth go dry and it's just as well – he can always just quench his thirst in her. "Or I'll make you."

"You will?" Cersei looks more disappointed than intrigued, to his great dismay. "A lover should promise the opposite, shouldn't he?"

"Oh, I only mean your words, sister," he elaborates, pride having been successfully stung. He's terribly predictable, he knows, but who is he to deny them both this rare pleasure? "As for any other noise you have to make, they'll hear you all the way in Storm's End."

Cersei scowls back at him, but allows him to push her back on the blanket of moss spread out behind her. It's getting harder to try and keep her skirts out of the way while he tries to tease a reaction out of her, so he just doesn't; reaches up and tears the laces of her gown open until it falls apart in front of him and he can look upon her as she is under the moon's watchful eye – skin nearly luminescent in the silvery light, her half-lidded eyes both impatient and wary. A pleased smile stretches over her features at his doubtlessly awed look and his sister laughs, laying her head back onto the greenery behind her. "Let us make them jealous of us both, then, shall we? Storm's End is ever so dull."

He descends upon her with a growl, his free hand running up the side of her body as his lips wrap around one of her nipples and Jaime grins when she gasps, her fingers turning into a fist into his hair. There you are, he coaxes, let me hear you. Let them all hear you.

He's never going to be able to get enough of this, he knows; had resigned himself to that realisation sometime ago, when it had occurred to him that he would devote his life to her without a second thought. He presses the heel of his palm against her heated skin as his fingers curl inside her and Cersei keens, high and desperate, biting her lip until her mouth turns unnaturally red in the scarce light the moon offers him – Jaime leans in to kiss her and the heavy taste of blood floods his senses immediately, and she makes another pleased sound as he sucks it off of her lips. To his surprise, it only makes him all the more eager.

He'd hungered for blood ever since this afternoon, when his sister had come to him, distraught, to tell him about the King's latest, and particularly grandiose, bout of disrespect. He'd asked if she wanted the man killed, but she'd refused, and he'd cooled off enough eventually to acknowledge the risks that she'd brought up – the Mad King had been one thing, but there's no way he's escaping with his head in its place from a second royal murder. Still, he'd imagined it well enough, and it had excited him nearly as much as the prospect of Cersei and their mutual retaliation does. For a moment, he feels the mad urge to tell her that she doesn't have to choose – he can kill Robert and then fuck her, too. He'd do it with the body of her husband still warm in the bed next to them if she wants; would do whatever she asks of him.

As it is, he'd accepted her alternative and had then endured Robert at dinner. She's a beautiful woman, your sister, he had said when the sister in question had deserted them under the excuse of preparing for bed, and he had stared at him rather intently all the while, as if Jaime had spent his entire life blind and had never happened to look at his twin. But cold, too; colder than anything. There are days when I have no idea what to make of her at all.

He'd nearly laughed in the King's face. Cersei is many things, and not all of them are terribly pleasant, but cold she had never been; if anything, the statement had only served to solidify his suspicion that his alleged brother by law has not a clue what he's talking about when it comes to women, no matter how many of them he's bedded. His sister is fire wrapped up in a woman's body; a living spark waiting for its host to spread like wildfire. She's the warmest thing he's ever felt.

"Jaime," she urges him now, her breathing fast and shallow, and he grins back at her when she presses up into his hand, greedy for more, always reaching for a release, or for further stimulation. She's so close that he can almost taste it and so he quickens his strokes to match her gasps, which only serves to make her moans all the more urgent. He loves it when she loses herself like this, no matter how short-lived it is, and she knows, because she glowers back at him, as if aware of what he's doing. "We don't have time to play games."

"Oh, I think we have all the time in the world." He frees his cock from its constraints, finally, and thrusts into her so quickly that it draws another delighted groan out of her as she welcomes him in.

"Yes," she says, but it's not an agreement – just an acknowledgment of the same ridiculous relief that had taken over him the moment they'd become one again. "Fuck me, Jaime, let the goddess see us if she so wishes."

It's so close to sacrilege that it only serves to thrill him further and his fingers dig into her waist as he holds her near. Jaime buries his face in her hair until he's as close to her ear as he can be; close enough to be heard over the sweet cries of her appreciation. "That's it," he goads her, leaving haphazard kisses whenever he can reach while still making himself heard. Somewhere in the distance, above her husband's ancestral home, a storm had gathered yet again and thunder crashes, the preceding lightning blinding him for an instant, making the picture that his sister sprawled out under him makes. He could spend the rest of his life just like this, he thinks, trying to get as deep inside her as he possibly could and watching her squirm for it. It's never quite quenched, this need to be needed by her, and his sister indulges it without complaint. "I told you they'd hear you in Storm's End, didn't I? I hope they do." He lets go of her back to hitch one of her thighs in an even firmer grip around his waist and a groan slips out, unbidden, at the minute change of position. His words run wild, no attempt at censoring himself lingering in the aftermath. "Fuck, Cersei. I want everyone in this useless little castle to hear you come. I want them to know what I've made you feel." I want them to know how inept their ruler is at pleasing their precious Queen. He hopes Lady Estermont hears, too, so that she knows what true pleasure feels like. From what he's gathered, she might have found more excitement if she'd gone to lay with her dead husband's tomb than with the King. He braces his knees against the soft earth below them so that he can thrust harder still, and Cersei arches up against him, head thrown back on another sharp cry. Her cunt squeezes him like a vice and he gathers her close again, nearly delirious, to bite his way up her chest and to her neck. Her blunt nails sink into his back as she clings to him, and Jaime can feel himself get closer to the edge of his release, too. "That's it." It's almost mindless in its repetition, but he doesn't have the capacity to care – he hauls his sister forward until she's draped over him, seated onto his lap instead of laying down, and the shift in the angle is going to be enough to bring her to completion, he knows. "That's it, fuck yourself on me."

"Yes," Cersei mewls in his ear, leaning onto his chest and drawing him into a distracted kiss as he thrusts into her from below. Her desperation for release laces every word and for a single, wild moment he wants to keep her suspended in the air between one breath and the next for the rest of their lives, if it means he'll get to keep her like this forever. "Yes, oh, Jaime. Stay, stay." He's not going anywhere and she receives a pleased, filthy grin for her efforts, which only makes her rush to explain herself further. She's terribly close; he can see it in the occasional flutter of her eyelids as she struggles to keep her eyes fixed on him; in the rhythmic hitch of her breathing; in the way she clenches around his cock, almost enough to make him come all on its own. "I want it inside me. Finish inside me, Jaime, I want— oh!"

He could live to a hundred years, Jaime thinks, and he'll never get tired of watching her come – the way her eyes widen, as if she's always taken by surprise, her lips parting on a moan, her entire body curling in around him to keep him near. And what is there to do, other than obey? Jaime clings to her and spills his seed inside her waiting body, the two of them collapsing back onto the bed that nature makes for them, satisfied, only a few moments later.

It doesn't take long for Cersei to get her bearings.

"That was folly," she says, breathing still rather laboured. "We should be wiser than that, Jaime. If we're ever to be discovered—"

"We won't be." Fuck wisdom, really. What's caution when compared to the sound of Cersei singing her praises in his ear as he fucks her? What's life when compared to that, truly? It would mean certain death, he's sure, but what a way to go. "I think your esteemed husband might genuinely be stupid enough to believe that any woman he's laid with would have eyes for no one else after that. I'm sure we're safe."

His sister seems to relax a little at that, leaning onto his shoulder, still stark naked in contrast to her worries. "We should get back soon."

"I'm tired of listening to what we should do," he says before he can stop himself and, just as Cersei opens her mouth to protest, he silences her with a kiss. "It's the Day of the Mother Above, isn't it? Let us celebrate, then."

The next morning is no holiday at all, and yet it finds them on that same beach, still wrapped up in one another, with Cersei sound asleep in his arms. Jaime doesn't mind at all – if the gods are watching as the folks of these lands apparently say, he hopes they're listening, too. His sister is his, as they should know now that she'd completed their ritual with him, and if there's any doubt about it at all, he's not afraid to make sure they hear her say so herself, loud enough for them to hear.