Mark and Kate's Dozen Rules

Meanwhile she whimpered when she felt it. The movement inside her went from a gentle caress to a desperate grab, squeezing down on him as he swelled, drawing the fluid out of him, her hips rocking involuntarily. Everything in them acted in choreographed concert towards the shared goal of procreation.

When he regained his senses, he realized that she hadn't reached her climax. Not quite.

"Sorry it wasn't enough for you," he said.

"Mm, it was plenty," she said.

"But I didn't get you off."

"You will," she said confidently with a smile. Even as he felt drained and spent for the moment, he could feel her squeezing around him, remolding him, bringing him back to life. This was yet another side of his sister that he'd never seen before. Whatever second thoughts he might have were still held at a distance as his longing for her quickly returned.

"I love you," he said, with a kiss.

"I love you too," she replied.

She guided him onto his side, so that she could take his penis, still slick with their shared fluids, into her mouth.

Before long, he had to pull her away. "Don't get me too excited. I don't want to leave you hanging again."

She climbed up on him, straddling his lap, lowering herself down onto his erection. He sank back into her flesh easily, and it felt like a perfect fit. She ground her pelvis down on his, rolling her hips back and forth. He leaned up, taking her nipple in his mouth. She cried out, her movements redoubling.

It didn't take a word to know when she was about to climax. It was good timing, because this was all nearly as overwhelming as before, and he was struggling to hold back. She screamed next to his ear as she lost control, her hips moving frantically on their own, everything inside her in high gear now. He lost control then too, his hands pulling her hips tightly down on his lap, as he drove himself up into her, his muscles straining against hers to get just that fraction of an inch deeper, to be just that little bit more likely to impregnate her. He swelled up inside of her again. Even though he had less pent up this time, he gave her all he had. When she felt it, her orgasm reached new altitudes.

She collapsed on top of him, her weight pressing her join on his cock, keeping them interlocked as her whole body shuddered, her breaths heaving in time with something inside her pressing down on him in rhythm.

---------------

Kate woke up in the hotel room, her brother cuddling up to her in his sleep. On the one hand, this kind of situation was starting to feel normal, routine, and pleasantly so. On the other hand, she felt aglow in ways she never had before. She knew how much further they'd gone the night before, further than ever before. She could almost feel the voluminous evidence still inside her.

It felt crazy that she'd dared to suggest having a baby to Mark. And that he'd actually jumped at the idea. And that he had now ejaculated inside her twice, deep in her vagina where his seed didn't have far to go, to reach her egg. And this was her most fertile time of the month. She could feel it in her bones.

She thought back on the previous night, recalling the feeling of his hot semen spilling into her, filling her, setting her off. She'd never had that before, not even on the sloppy, drunk, clumsy occasion that led to Emma. She hadn't known feeling a man cum inside her could feel like that, but it also probably helped that she knew what it meant. She knew what could happen, and she was welcoming that possibility with her whole self.

She half expected herself to be appalled in the morning at what they'd done, and do whatever it took to prevent it. But she certainly hadn't hit that point yet. Yesterday, the idea of having a baby with Mark had been just a fantasy; she hadn't known if it could ever be real. Now it was much more than that. It was definitely a real possibility. It might even be already set in motion.

Kate felt Mark firm up, spooning against her back. Whether she was still slick from last night, or getting hot again this morning, she managed to slide him between her thighs from behind, until the head of his cock nudged into her. She felt his arm reach around her, holding her tight as the sensation roused him from sleep. They had come to this brink plenty of mornings, but normally they had to stop before the edging got the better of them. Not today.

Mark's hand shifted to her hip, and his cock pressed deeper into her from behind. She leaned forward, lifting her leg to give him an easier angle to push further. By now, she was used to the feeling of him inside of her, of feeling how his anatomy filled hers. This was the same yet different. She could feel every ridge of him, every little movement, every muscular contraction, every jolt, every swell.

She half-longed to roll him onto his back and ride him again, but she also enjoyed the relaxing, slower pace of this. He pushed into her and withdrew unhurried, simply enjoying the moment. They no longer had to rush to the finish line. The race had already been won. This was more of a victory lap.

But it couldn't last forever. She could hear the intensity of his breath from behind her shoulder. It was most welcome when he reached down between her legs, to where their genitals met, and started to tease her clit, the way he'd learned from her an entire year ago. She didn't realize how close she was until she noticed that he was carefully keeping her just on the edge. Reaching back, she grabbed his thigh, urging him on.

"Do you still want it?" he asked.

"Do I want what?" she asked, teasingly, to make him say it.

"Do you want your brother to knock you up?" he said, and an unconscious thrill went through her at the words, at the idea. This was really happening. Maybe already had. It reminded her how beyond reason it was, and yet she did want it.

"I do," she moaned, as he kept thrusting into her. Hoping this would be enough to put him over the edge.

She realized this was the second time in a day that she'd said "I do". Maybe it would be worth revisiting whether they could get married somehow. They were only step-siblings after all. They weren't related by blood, not yet anyway.

"I want to hear you say it," Mark whispered into her ear from behind, holding her close. She could tell he struggled to get the words out. He was just barely holding out. She was close too, and knew just what she needed.

"Cum in me," she urged him. "Knock me up. Get your sister pregnant."

He grunted loud, unable to choke it back, holding her thick, pudgy hips against his. With nothing between them, she could feel the shape of him, nestled inside her just right, his tip just barely nudging her cervix, where one child had already emerged from her womb. She felt as his cock became stiffer, larger, engorged in preparation, pressing out against her walls, making her feel even fuller.

Then came the flood. Maybe it wasn't as much as the night before, but she still felt it splash into her, warming her from the inside. She cried out, clenching down on him. His grip on her hips tightened; he was determined not to budge from this perfect union until the mating dance between their bodies was complete. When her orgasm set her interior muscles into motion, he gasped hard, right by her ear. She knew he could feel it, especially when it made him swell up again and pour more of his seed into her, another wave on the beach as the tied came in, rising higher every time. Now the undulations inside her were unconscious, something primordial taking control and working hard at extracting his genes and sucking them deep into her.

Even as they laid there still together, nothing inside them was still, as she trembled and shook and he strained and gushed into her over and over again, until she drained everything he could give. Then they collapsed together, exhausted already, their bodies still conjoined, still in position to go again.

"So that rule about no one ever knowing..." he said. "Don't you think it's going to be pretty obvious?"

"We haven't broken that rule yet," she said. "Last time I got pregnant, it was from a casual one-time thing. People might believe it. Though...the idea of other people finding out about us...to be honest, it kind of turns me on."

"I can tell," Mark said, and she could feel him firming up again inside her. She had never felt that before. It was yet another new and exciting sensation.

Eventually they made it to the hotel breakfast buffet, just before it shut down. Kate was famished like she'd ran a marathon.

"Feel like I'm eating for two already," she said.

Mark laughed. "Thanks for saying it, because it took a lot of effort not to make that joke myself."

The truth was that she just felt incredible, still somehow riding the high of their explosive love-making. But she was also thinking ahead, her eyes drifting out the window of the hotel dining room towards the horizon.

"You miss Emma already, don't you?" Mark asked. "Me too. It's okay, we can check out and head back home."

"No need to rush. We've got the room until noon," she said with a smirk.

----------------

Mark refilled the cooler with a mix of beer and non-alcoholic options, and he lingered a minute in the house, in the quiet, just to decompress and reflect. He didn't want to go back to the party just yet.

Life was coming on fast these days. Kate was pregnant. It might have happened on that anniversary weekend, or any of the many times thereafter, there was no way to know for sure. Even when they came back from that trip, their sex life had shifted into high gear, now animated by a shared secret, a shared purpose. Like with every rule they had made for themselves only to break, there was no going back, and no regret.

Kate's condition wasn't a secret anymore, though. It started to show sooner than it had with her first pregnancy, since we was fitter to start with. Now there was a recognizable curvature to her middle.

They got married too. Went to the a courthouse in the city, with a quick civil ceremony in front of a judge who didn't know who they were and didn't care how they had ended up together. Nowadays there were some folks who knew them as husband and wife, and there were still others who knew them as brother and sister.

This baby shower was a big deal for them. Not only were they celebrating the impending birth of their child, but this was a chance to see what people around them thought of the whole thing, and to try to clear the air. They had thought about just pulling up stakes and moving somewhere new, but there would be no escaping their past forever, and it also wasn't something they were ashamed of.

Up to this point, they could have still kept their rule about not telling anyone, but today their relationship was on full display. Mark found it scary and exhilarating and unbelievably sexy.

Mark steeled himself and rejoined the baby shower, coming up beside Kate and giving her a kiss on the lips.

"Ahem. Mark, you remember Mrs. Rankin, from elementary school?" Kate asked.

Mark froze. Of course he remembered the strict disciplinarian they'd both had for fifth grade. Mrs. Rankin was much older now, but she still carried the displeased look he remembered. He knew the look. She knew they grew up together. It looked like Kate was trying to have a different conversation with another guest.

"Oh. Hello Mrs. Rankin," Mark said sheepishly. Even as an adult, it still took all his courage to face her down. "Let me get you a drink, and we can catch up on old times."

Mark pulled Mrs. Rankin aside and explained the situation, for the umpteenth time. How they weren't actually related, how they had ended up together despite the odds. Mrs. Rankin started to lighten up when he got through to her. Not that she was ever going to give her blessing, but maybe now she at least wouldn't cause a scene at the baby shower.

"Daddy! Daddy! Daddy!" Emma yelled, peeling off from the group of kids to run up to him. He scooped her up into his arms.

He had stopped correcting or amending her when she called him that. Sure, the two grandparents who were married weren't the ones she'd expect. Sure, Kate had conceived her with another man who wasn't part of her life anymore. But these were the kinds of details that a girl Emma's age didn't need to understand right now. For now, Kate and Mark could just be her mother and father, with a baby brother on the way soon. Emma didn't need to know right away that the baby would be her half-brother. Mark and Kate had grown up treating each other like normal siblings, and they wanted that for their kids too.

Mark was physically sore that night, after the party, after getting Emma to bed. But when he got to Kate's bedroom, Kate was already getting started without him, her fingers down under the sheets, her face a mix of distraction and concentration and pleasure all at once. She was a sight to behold, and he stopped in the doorway.

When she noticed him there, she asked, "What are you doing?"

"I thought I was supposed to stay over here and just watch," he said, recalling that first time he'd watched her get off.

"Get over here, you goof," she said, throwing a pillow at him. He caught it and brought in back to her, sinking into bed next to her.

Mark ran his hand over his sister's belly, and down to her crotch where her hand pulled his to where she needed it. As he did so, he felt the baby kick. It felt a little odd sometimes, like the two of them weren't really having sex alone.

Kate was soaking wet and ever so sensitive tonight, as she often was these days. It was a wonder that she somehow got through her first pregnancy without a helping hand.

She leaned towards him, and he murmured, "Oh? So we can kiss now?"

Her lips met his, tenderly at first. "Good one. Did you hit your head or something?"

"You don't seem tired yet," he remarked, ignoring the jibe.

"You know how Mrs. Rankin was giving us the stink-eye today?" she asked.

He kissed along her shoulder, down her chest, giving her nipple a lick, making her shudder. Her breasts had swelled up again. She weaned Emma off breastmilk a while ago, but it wouldn't be long until Kate was breastfeeding again.

"That's...gonna happen sometimes," he said. "It's a small price to pay."

He kissed taut skin of her belly, sparing a kiss for the child growing inside. Meanwhile she knew where this was headed and reached for his erection. Somehow, even long after they discovered other delights together, he still never tired of her touch. His cock spasmed in her hand.

"I'm not complaining," Kate said. "Actually...it's kind of exciting to be reminded about what this looks like to other people."

"Like two siblings having a baby together?" he asked, as he made his way lower, until his tongue reached her slit.

"Yeah, just like that," she replied breathlessly, melting as he lapped around her clit.

Mark felt her hot breath on his thighs as she leaned over to take him into her mouth. He moved himself to meet her halfway. For a moment, it distracted him from his own mission, the shear warmth and wetness and friction of her tongue on him. She was more practiced at this than when they'd started, more attuned to what worked on him. Almost too good at it.

He tried to focus on what he was doing to her, which helped for a little while. One of her hands reached down and held his face to her crotch as she came. But it was only a minor orgasm, compared to what they now knew was possible.

"Mm, no bodily fluids, right?" he warned her.

"Not yet at least," she said.

He repositioned himself looming over her, careful not to press on the mound of her belly. At first he just ran his erection up and down the length of her labia, coating himself in her juices. There was no fabric between them to start with, they had skipped right past that stage tonight, but sometimes they visited it. She pressed her crotch back against him, trying to find the right angle where he'd slip inside her. Still he held out as long as he could.

"I need you inside me," she finally said. It was a command, but her desperation made it sound more like a request.

"I guess I'll need a condom then," he teased.

"Too late for that, in case you haven't noticed," she replied.

She got up and climbed onto her hands and knees on the bed. He slipped into her from behind. This was one position that put little pressure on her belly, and let him give her all he had. He slipped into her from behind, her tunnel welcoming him back in, caressing his length. She whimpered as she felt him part her flesh.

He gripped her hips as he started to thrust into her, slow and steady at first, savoring every push and pull inside her as they parted and rejoined, his cock seeking out that perfect spot inside her to deliver his seed, as if she weren't already pregnant with his child. But the sensation was all so much, and he could tell that for her it was not quite enough.

It took all his willpower, but he withdrew from her long enough to lie down on his back, for her to straddle his waist. She guided him back up into him, and lowered herself down on his erection until she was sitting heavily on his crotch, his penis as deep inside her as it could go. He had never been with a heavier girl before Kate, and so it had surprised him how good it felt when she did this. Now she was that much heavier still, making their union even tighter.

Then she started to roll her hips, her clit pressing against him, her vaginal walls massaging him inside her. Not that she was focused on him, she was in a world of her own. He could tell she was desperately close, she just needed one more thing, that only he could provide, and it wouldn't be long now.

"Do you still want it?" he asked teasingly, reaching up to grab her breast.

"Knock your sister up, you incestuous perv," she moaned, shortcutting their usual script. "Make me yours." As if he hadn't already.

Ever since they'd crossed this threshold, it seemed like feeling him ejaculate inside her was something she almost needed to get off. It certainly made her cum harder than anything else. Mark wasn't sure what they'd do after the baby was born, when pregnancy would eventually be a risk again.

At her words, he couldn't contain himself any longer. With a grunt that he struggled to contain, his hips bucked in synchrony with hers. He felt himself engorge more fully inside her. She kept rocking her hips, the sensation almost painfully overwhelming at this most sensitive moment for him.

She could feel what was happening, what was impending. She had become so familiar with the signs and the sensations of it. Her orgasm crested just a breath before his semen flooded into her. At the feeling of it, her thighs tightened around his waist, her vaginal muscles bearing down on him, stimulating him to swell and pour more into her. Kate rutted like an animal in heat, and it was all Mark could do to hold on through it all, as she tugged and squeezed him, as his cock spurted again and again. She kept rocking forward and back until he was completely spent and she completely sated.

Eventually, Kate lifted herself off him, and lay down beside him in the bed.

When eventually he could speak again, he said, "I'm afraid I might pass out in your bed."

"Very funny," she said. "I love you."

"I love you too," he said, and put a hand on her belly again. "Both of you."