Mark and Kate's Dozen Rules

It didn't help matters that Mark was still around, as always. Though in the aftermath, he had definitely backed off. He was spending more time alone in his room now. She started wearing less around the house, leaning over the counter to entice him, trying to get them alone together on the couch again, but it wasn't getting through. He seemed completely oblivious, and she was still scared about making her needs known, especially when they were so taboo.

Though she also wasn't entirely sure what kind of reaction she was looking for. This was her brother after all, someone she shouldn't be trying to entice in the first place. She was scared of sending too strong a hint, prompting him to take it too far. She was starting to suspect that for every line they crossed, there was no getting that line back later.

What had kept them apart for so long was the assumption that they couldn't be attracted to each other. Categorically. In either direction. Now they knew otherwise, and that was dangerous knowledge to have. Now it was a question of how far they'd let this go. The temptation would always be there. Where would they take a stand against it?

The exchange of bodily fluids aside, Kate found herself feeling okay with the things they'd done so far. Masturbating together, even masturbating each other, this was all relatively safe, if not innocent. It gave them a way to get off, to get out that sexual tension, without risk or long-term damage. And even though she had subsisted on just her own touch for so long, now she hungered for something more. Maybe they could indulge this, in a very limited way, and someday this would all be just a brief, weird phase of their much longer shared past together.

Mark was in his room again, when she knocked on the door. He didn't answer right away, but she didn't expect him to. She knew what he was up to in there, by the sounds of porn leaking from his headphones.

She opened it a crack. "Need a hand with that?" she asked, cringing at the corny line.

In a hurry, he stopped the video and shoved the phone out of sight. Funny that he was embarrassed about that, but didn't move to cover himself up. They were past modesty now. "Oh...I thought you weren't..."

"I was pretty freaked out for a little while there, yeah. Maybe I did need some time, but I'm ready to pick up where we left off, if you are," she said. She sat down on the bed, across from the chair where he sat. "Look, we're each just trying to get through a dry spell right now. Given the situation, I don't see any serious harm in helping each other through that, just for the time being. But there need to be rules. This can't be a slippery slope."

"It felt pretty slippery to me," he joked. She rolled her eyes. "I mean, sure. Your house, your rules."

"Our house, our rules," she corrected him. "You get to have boundaries too. Anyway, rule number one, no genital-to-genital contact."

Mark nodded. "Given what happened, maybe we should also have a rule against exchanging bodily fluids."

"Good point. That's rule two. Rule three, no kissing. I know you haven't tried to, but still. Gross."

"Yeah, gross," Mark said. "My turn. No one can ever know."

"Naturally. Wasted your turn, if you ask me," Kate replied. All this talk of what they'd be doing together was getting her even more worked up. She slid a hand up his leg. "Rule five, we are not going to start sharing a bed."

"Good," Mark agreed. "No acting like we're in a relationship. Not even in private. We have a relationship already, as brother and sister. This other thing can just be platonic."

"I don't think that means what you think it does," she suggested.

"Whatever. Physical, not emotional. No valentines, no date night, none of that gushy stuff."

"I'm glad we're on the same page," she said. He had said his piece, and she felt more comfortable with their boundaries in place, and knowing that he wanted the same things out of this that she did. "That makes this so much less complicated."

She knelt in front of him, taking his erection in her hand. Then before he could object, she lowered her head down to his lap, taking him into her mouth. His breath hissed out sharply. She could feel his thighs trembling with unfulfilled desire.

"I guess...we don't have to...count that...as a kiss," he said, struggling to form words. She grinned wickedly.

He ran his fingers through her hair, and she could feel the tension building in his loins. But then he stopped her short, with a hand under her chin.

He undressed her and guided her onto his bed. It was the same one since their childhood, and it creaked alarmingly under the weight of them both. He laid down opposite her, and as she took him back into her mouth, she felt him probing her crotch, eventually bringing his face to her slit. Her thighs came gently to rest on either side of his head, as his tongue sent electric thrills through her.

"I guess we don't have to count that either," she said, just to voice her approval. She pulled his face closer to her crotch, as a wave of her orgasm hit. Only the first wave though.

"I'm getting close," he said, and she pulled him from her mouth.

It took only a few more strokes of her hand, before his seed came pouring out. Most of it fell directly on the bed, but some also reached her cheek where she let her head rest. She was too drunk on her own ecstasy to care.

Through it all, he redoubled his lapping at her clit and she humped his face until she came, harder this time, her hands clutching his waist tightly to herself.

When she came down from her high, she disentangled from the bed and from him. He looked dazed, with a satisfied smile on his face. She got up and washed his semen from her cheek. She felt satisfied and refreshed and no worse for wear. It was almost looking like an ideal arrangement.

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Mark woke up to the sound of Emma's cry, and he stumbled groggily towards the nursery.

"I'm on it," he called out as he passed Kate's doorway, although from the sound of her breathing, she probably wasn't awake yet. Maybe he could let her get some rest for once.

He could tell Emma needed her diaper changed, so he did that, and then he washed himself up. She wasn't interested in a bottle, so he put her back in the crib.

Now Mark was awake in the middle of the night. Too awake to get back to sleep right away. He slipped into Kate's room. She was sprawled out on her bed, under just a thin sheet. Even in the faint light through the window blinds, she was gorgeous. Sure, she was ticker than other women he'd been with, but it only accentuated the curves of her feminine form. How had he managed not to see it for so many years? Now they were getting each other off on a regular basis, and he wouldn't have it any other way.

He pulled the sheet aside bit by bit, and leaned down to kiss the skin he exposed. It was against a rule, but only a minor one, and it would only count if he got caught doing it. He reached her full breasts, and then the broad plain of her belly, a belly that had already borne fruit. Her abdominal muscles went taut under his kisses. His hand slipped under the hem of her underwear.

"I guess we can say this kind of kiss is okay," she whispered in the dark. "But no mouth-no-mouth."

"Only if you need CPR," he replied.

Her hands sought him out in the dark, pulling him into the bed with her, as her arousal woke. She caressed him, teased him until his body was yearning for hers. He slipped out of his shorts easily. She was soaking through her underwear, and he started to pull them off, but her hand stopped him.

She rolled him onto his back and straddled his waist. He could feel her weight on him, but he liked it. It pushed down on him harder, forced them closer together. Her soaked underwear pressed against the underside of his shaft where it lay against his stomach. He could feel her heat and her moisture. She started to move back and forth, pressing her slit against his shaft through the fabric.

"No genital contact?" he asked, to gauge if she had changed her mind.

"No, we're not touching, are we," she said as she rode him.

"Mm definitely not," he conceded, reaching up to cup her breast.

"Don't cum until I'm ready," she said. It sounded like an order.

"That better be soon," he said.

"It is," she said, her rutting redoubling. Soon she cried out.

He suspected she wouldn't have stopped for anything by then. Nevertheless, he grit his teeth, trying to hold out just a little longer, while her orgasm kept going.

"Oh god, Kate!" he gasped, and felt his own hot fluid spread out across his stomach. His hands instinctively gripped her hips tight to him, but she backed off enough not to get caught in the flood.

Everything went a bit hazy after that. He didn't mean to fall asleep there, he just did. And when he woke up in her bed, with her in his arms, it was so perfectly comfortable that he didn't want to move. In fact he didn't want to do anything to disturb the situation, despite the morning wood he had pressing into her backside.

Kate clearly had other ideas however. She was pressing herself back against him, pulling his hand to her breast.

"Sorry for falling asleep here," he muttered.

"Don't make a regular thing of it," she said. "You only get to pass out in my bed when you make me cum like that."

"Who says I can't do that regularly?"

With a little careful alignment, he felt himself pressing into the soaked fabric of her underwear again. First rubbing his shaft along her slit, then pressing into her hole, as far as the fabric would stretch.

"You probably don't want me cumming like this, fabric or no fabric," he said.

She pulled away from him and slipped them off. "They were seriously starting to chafe anyway."

Rolling to face him, she hooked one of her legs around his, pulling him close again, until he felt his erection nestle in her slit.

"No genital contact?" he asked.

"Ugh. New rule. No penetration," she said. "I mean it."

They pressed against each other, his shaft slipping against her, pressing her clit with every thrust, this time with nothing between them. Mark thought he was going to be able to get her off first, and maybe withdraw before anything risky happened. She was so close, clearly beyond the point of self control. But the feeling of her directly against him was too much. He felt it boiling up from within him.

"Mm. Kate!" he cried. "Kate!"

The head of his cock was mashed between her stomach and his, and his semen spread out between them. From her keening cry, he knew she couldn't bear to stop now. She kept pressing herself against him, until with a desperate squeal, she finally came, her hips bucking against his, her every breath a choking gasp.

When they finally pulled apart, it was a sticky mess. It was hard to tell which was her juice, which was his, and where the two had combined. They couldn't be absolutely sure that none of it had reached her. So she had to go out and get another emergency contraceptive.

When she got back, she handed him a box of condoms. Mark looked at her, surprised. He had expected them to back off again after what happened, not escalate further.

"Here. It's not contact if there's latex in between," she explained. "I can't keep taking these morning-after pills. They ruin my business for days. Plus people in town talk every time I show up to buy one. Better this than that."

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Kate got home from a pleasant night out. She'd gotten to catch up with a friend who was visiting town. Mark had offered to babysit Emma so she could go out and enjoy herself. Which worked out well, because Kate wasn't entirely sure how well she and Mark would be able to hide their affair anymore.

"How'd she do?" Kate asked as she hung up her coat and her handbag.

"She was an angel," Mark said with a smile. "You made a great baby."

Kate looked at him, surprised yet again. Growing up, they were always fighting, but she'd started to see a whole new side to him lately.

"Okay. Get up," she said.

"What for?"

"We're going to the bedroom," she said, offering him a hand.

He stood, and for a moment they stood there, almost pressed against each other, and she wondered if they'd even make it to the bedroom. This was when a normal guy would kiss a normal girl, but they'd said no to kissing. The moment passed, and they went to her room, stripping quickly.

He put on a condom. Up until now, they were just a precaution, a very useful and effective one, against letting his seed splash around between them. She'd said no penetration, and he had respected that. Another point in his favor that she almost couldn't stand.

Now when he climbed onto the bed with her, she just said, "I'm ready."

"Ready for what?" he asked, half-teasing. She reached down, grabbing his cock, guiding it to the precipice of her tunnel. She even gave his buttock a playful slap to urge him on. "Oh. Oh my."

So for the first time, he pressed into her, little by little. When he withdrew, it was like he took her breath with him. She needed him back inside her. She felt like she wouldn't let him withdraw without knowing he'd be back, pressing a little deeper each time. To places not even his fingers had reached. Places maybe no one ever had. They were conjoined ever tighter, until there was nothing left between them.

"I'm glad this doesn't count as genital contact," he joked. "Wish I'd known earlier."

Instead of responding sarcastically, she just said, "Me too."

This was a spur of the moment whim, and she wondered if she'd come to regret it afterwards, but in the moment, it felt disconcertingly natural to have her brother fucking her. Maybe not quite fucking. Making love.

Whenever she'd thought about it before, she'd thought this would be too much, this would be the step too far, this would be the one she couldn't go through with. But after everything they'd already done, it wasn't much of a stretch at all anymore. It was a long-awaited culmination of what she knew they both wanted. They had teased this possibility so many times and stopped short, so there was no more shock to be had here.

He started moving again. While this wasn't all that different from what they'd done before, this was filling a slightly different need, one that had grown larger than she realized. She had needed this, she'd been missing this, so badly. She let herself moan and writhe under him, her breath hot across his ear.

She ran her fingers through his hair, pulling his head up, so that his eyes met hers. They had seen each other approach orgasm many times by now, something brother and sister were never supposed to become so familiar with.

She chewed her lip, the pleasure almost too much to keep at bay, but there were other things she wanted out of this, this time. He was close too, his thrusts going from patient and measured to desperate and instinctive. Then he pressed himself deep into her, clutching her tight in preparation for what would inevitably come next. In that moment, she pulled his face down to hers, kissing him hard on the lips, her tongue dancing into his mouth.

It was another unexpected intimacy and transgression, another wild sensation at a moment of overwhelm. When he swelled up inside her and flooded the condom's reserve with his warmth, it triggered a time bomb deep inside her, a riot of muscle motion. It wasn't his warmth that flooded her, but she still felt flush all over.

He moaned through her mouth, his hands shaking as he struggled to keep his grip on her, struggled to keep himself pressed as deep into her as he could go. They had never been conjoined like this before, and it was a special feeling, one they both desperately wanted to last. Her frame went taut under his, holding him tight to her, before she lost her grip and lost control completely.

"Oh my god," was all she could get out in words.

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

Kate couldn't entirely sleep through the sounds of Mark and Emma up and about. Her little girl was an unfortunately early riser, and starting to be more perceptive about what was going on in their home. Emma had already started calling Mark "dada". Emma was more mobile now, more energetic. Harder to coral sometimes. She didn't cry in the middle of the night so much anymore, but she took a lot of attention in her waking hours. Fortunately, Mark had stepped up, juggling a part time job with daytime childcare.

Lifting her head from her pillow, Kate found a note on the nightstand. "Happy Valentine's Day! Sleep in, Kate".

She smiled, her eyes stinging with the threat of tears. Yes it was against the rules, but it was even more touching for it. Neither of them had wanted or expected for it to end up like this, and yet here they were. She'd been the one to kiss him after all, and once she started, she didn't want to stop. Now they were affectionate around the house all the time, except when they had visitors. She loved feeling his hand on her back whenever he came up behind her. She enjoyed the look on his face when she'd slyly grope his ass.

By now it really was like they were in a relationship, in all the ways that mattered at least. Yes the sex was great, although there were certain things they still held back. But in so many other ways too, Mark was the kind of boyfriend that Kate had never had before, the kind she'd never really dared to hope for. It was like she had won the dating lottery without even playing.

But like every blessing in her life, it came with a catch. A nuclear doomsday clock stuck at one minute to midnight for so long that the danger almost didn't feel real anymore. She wasn't sure that what they had could ever be public or official or legal or even mentioned amongst friends. Besides, if things went sour between them, there'd be no easy way back to where they started. She'd risk losing what little family she had left.

As sexually active as they were, she still found herself getting hot in moments alone like this. She had never felt so sexy before. Her bulky frame had made her mostly ignored during high school, except when guys thought she was easy, thought she was fit to use. And that had been before having a baby as a teenager. She'd been sexually active before, she'd been horny and fertile and getting fitter by the day.

But being with Mark had awakened something inside of her that not even conceiving her daughter ever had. It was a whole different thing, sharing intimacy with someone she knew all her life, someone she trusted, someone she loved, for values of "love" that she didn't dare evaluate.

From the other end of the house, she heard Emma's exuberant babble, and then the sound of the front door shutting. It sounded like Mark was taking her out, maybe for a trip to the playground.

Now Kate lay in bed feeling her body come alive under her own touch; she finally had a face to play the role of lover in her fantasies. Even her wildest ones, the ones that came to her unbidden, despite herself. The ones where there was nothing between them at all, except for love and desire. She found herself imagining letting it go too far, feeling him cum deep inside her, crossing that final, irreversible line, welcoming the spark of another life into her core, where she knew from experience that it could flourish.

Yes it would be a bad idea, a disastrous one, but exactly how disastrous? An earthquake? A tsunami? In her fevered state, she knew her mind wasn't in a place to think things through, but there was no harm entertaining the notion when she was alone.

Except she wasn't alone after all. The bedroom door opened, and Mark slipped in, and started stripping out of his sweats. It wasn't that long ago that the sight of her brother naked had still been a shock to her. Now they were hardly shy about seeing each other this way.

"You got a head start," he remarked.