Mark and Kate's Dozen Rules

Mark was having a dark night. It was his twenty-third birthday, and and he thought going out and having a drunken one-night stand would be a blast. He thought it would help him get over Stacy, who had left him alone with this downtown apartment to pay for by himself. Instead, it felt weird, having sex with a stranger, even if she was almost as cute as her profile pic. It left him feeling even more alone and helpless.

He couldn't go on like this, especially since his job had unceremoniously laid him off. It wasn't anything personal--they laid off a couple hundred people that day, and despite meeting his sales quotas, he was still fresh out of college in an entry-level job. Not anymore.

The apartment was still mostly furnished--Stacy hadn't brought much when she moved in and hadn't left much when she left Mark for another guy--but it still felt half-empty.

He'd started job-searching, when could motivate himself to. Just like he'd started dating when he could motivate himself to. But it might take months to land another under-paying job, and he didn't have months of this left in him. Same with dating. A couple weeks ago, he had it all, now he just wanted out of the system altogether.

Still buzzed from drinks at the restaurant, Mark decided not to reach for another bottle. Instead, he got to thinking about what his life had been like, before college out of state, before the big city job.

He picked up the phone and called home, to the old landline. He desperately wanted to reach his parents, but that was impossible. They died in a car crash a year ago. It still took him by surprise sometimes, especially when his mind wasn't moving full speed. That left just his sister Kate in the old house, and her baby daughter Emma. He hadn't meant to bother her in the middle of the night, but the call was already ringing.

"Mark?" his sister Kate answered.

"Hi Kate, sorry to wake you," he said.

"Whatever. I was just up to feed her," Kate said, sounding annoyed that she couldn't be annoyed. "You're drunk."

"I'm drunk," he confirmed. "It's wearing off though. Kate, I need to come home."

"Don't you want to sleep on it?" she suggested.

"I'm sure about this. I don't know what else to do," he said. He struggled and failed to stay composed.

There was a pause at the other end, then a sigh. "Yeah. Okay. But my house, my rules, okay?"

"It's technically our house," Mark said. "...Fine."

They inherited equal shares in the family home. Though Kate was the one living there when their parents died, and she had done most of the work of sorting out their parents' estates. Mark had been living further away, had a more demanding job, etc. Now those just felt like excuses not to be bothered. Not to confront the heavy stuff head on. Now he regretted missing out on it, and he regretted putting Kate through it alone.

"Get some sleep, Mark," Kate said, and then she hung up.

He wasn't entirely looking forward to living with Kate again. There had been a time when they got along okay, but that was long ago, before the years of teasing and bickering and fighting over everything. Food, cars, television time. It was all so petty. He worried he'd fall right back into those tired conflicts.

He also wasn't sure how well he'd handle living with an infant. The last infant he'd lived with was Kate. At least this would allow him to make a clean break with this dead-end situation. He could move back home for a little while, get his act together, and start over.

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Kate heard Emma cry, and hit pause on her online course. She quickly slipped out of one side of her baggy t-shirt, and picked Emma up, offering the baby a nipple. Then she realized Mark was in the room, grabbing snacks from the pantry. His expression was hard to read. Was he scandalized? Was he staring? Kate rolled her eyes.

"What. You've seen a breast before," she said. "Baby's gotta eat."

"Sorry. You're right," Mark said, wrenching his gaze away from her exposed chest.

It was different, having him around. Not better or worse necessarily. Sometimes Kate felt more self-conscious about walking around the house with hardly anything on. Other times, she felt like she shouldn't have to cater to Mark's sensibilities. Her house, her rules, after all.

It was one more abrupt shift in her life. Just a couple years ago, she had graduated high school, she was planning to go to college in the fall, and then over the summer found out she was pregnant, and pretty far along by that point. She hadn't noticed right away because of her weight and her history of irregular periods.

Kate knew when Emma must have been conceived, from an abysmal hookup at a party that she'd thought nothing of at the time. She'd been on the pill, but her fat-phobic doctor prescribed a dosage that apparently had all of the side-effects and none of the benefits. She stopped taking it and never went back on. Big girls were also supposed to have trouble conceiving, but it turned out she couldn't count on that either.

She cancelled her college plans and gave birth to Emma that fall instead. She was lucky to have supportive parents in those early months, but then they'd both died in the crash. Between their inheritance and life insurance, she was getting by, but now caring for Emma was all on her, in a house far from neighbors, far from even a small town, where everyone knew about her and her senior year baby.

Now she had Mark around. He at least helped out, with things like dishes and keeping the house clean and picking up groceries. There were things he seemed reluctant to do though, like cradling the baby, bottle-feeding her, changing her. The house wasn't so quiet and empty. He was always somewhere doing something. They had to take turns showering, take turns using the treadmill.

He was a still young adult guy too. One of her first rules was that he not bring dates around here. She didn't want to deal with it, didn't want them waking Emma. But she knew he spent time in his room alone for a reason, sometimes on a daily basis or more. Not that she could blame him for that, it was only natural to need release.

After her online course was done, and Emma was laid down for a nap, Kate had a little while to herself. When she had the house to herself, she could do this all she wanted, but now she cherished the opportunity for self-pleasure.

She laid out on her bed, tracing lines across her stomach with her fingers, and up around her breasts, biting her lip as her breath caught. She was normally very vocal, even by herself, but she had to keep it in nowadays.

She tried to picture herself with a lover who didn't exist. She was determined not to let the role of father be a rotating cast in Emma's life, and there was no one to date around here anyway. When she imagined scenarios playing out, sometimes it would be characters from TV. Sometimes, in moments of shame and desperation, it would be Mark. She told herself it wasn't attraction, it was just her mind filling in a blank with the nearest example. Though this wasn't the Mark she remembered from high school. This Mark kept better care of himself.

When her hand followed her thigh to where she was already wet and worked up, a moan escaped her lips by accident.

"Kate, I'm just going to grab a..." Mark hollered from out in the hall, as he pushed open the door.

She realized too late that she'd forgotten to latch it, let alone lock it. While living alone, she'd lost the habit. The door swung open, and Kate found herself frozen in surprise.

Mark stopped in the doorway, looking at her spread form, her hand on her clit.

"Oh. Sorry. I didn't realize you were...in here..." he stammered. And yet he finished the sentence without leaving, his eyes stuck to her like glue. She wondered what he saw there. Something appealing? Something grotesque?

She knew she ought to stop, she ought to cover herself. But why should he get to interrupt and spoil it? This was her time.

"You're such a bad liar," Kate said. "You knew I was in here. You knew what I was doing."

The blush on his face was confirmation enough. Also the growing tent in his shorts.

"You wanted to see your sister masturbate," she accused him, the thought surprising her even as she said it.

"Step-sister," he corrected her. They hadn't made that distinction in quite a while. He shrugged. "I mean...you are a live, adult, female human being."

This shouldn't be happening, but it was happening. He had already seen her. He had already caught her in the act. He knew what she was up to, meaning that he had already heard her on prior occasions.

So what was she to do about it? She had to admit that the two of them being cooped up here was making them both a little stir crazy. Might as well roll with it, as long as there's no harm done. Maybe just the once.

"You want to watch? Fine, you can watch, but that's all. You stay over on that side," she said.

Now when she touched herself, she didn't have to be quiet on account of him. She let herself moan and gasp, and she noticed despite herself how his erection grew, how he leaned against the edge of her dresser for support with white knuckles. But she still felt like this wasn't fair. It was too one-sided, expecting only her to expose herself like this. They should be equally to blame.

"You know what? I change my mind. If you're going to stay, you have to do this too," she said.

She stopped stroking herself for a moment, until her words sank in. He stared at her in disbelief. Whatever he had expected to happen, he didn't seem ready for this. Not that she felt prepared to see her brother masturbate either.

"Go on. Pull it out," she instructed. He dropped his shorts, and the erection sprung free. It wasn't the first time she'd seen one, but it was the first time she'd seen his hard. "Well? Are you going to actually stroke it?"

At her teasing, he did start to run his hand along its length, and she resumed fingering herself, gently, cautiously now, since she was so close already. She teased herself, edging up to climax and backing down again, as he looked on. This felt wild, forbidden, insane. The room felt warm, almost intoxicating, filled to capacity with lust from the two of them. And yet, she didn't want to finish first in front of him, and let him run off and finish himself in private.

Abruptly he grunted, like it had snuck up on him. Milky fluid poured from his tip, running down over his gripping hand and dripping onto his shorts below. His knees buckled under him, his balance straining.

Seeing his orgasm overtake him had a surprising effect on Kate too, bringing on the full force of the climax she'd teased herself with. Her thighs clenched around a lover that wasn't there, her whole body shaking, her pleasure rising from her throat uncontrollably, her free hand gripping the bed sheet hard. Her eyes rolled back in her head.

By the time her vision cleared, Mark was gone. That was probably for the best. They had definitely crossed a line, even if it wasn't a major one, and she wasn't ready to talk about it. She wasn't even really ready to think about it just yet. Not with her guilt and worry tied up in the intensity of what she'd just felt.

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Mark was trying his best to act like everything was still normal. Like they were still normal. To set aside the knowledge that he and his sister had masturbated together. He had seen her naked, smelled her scent, watched her touch herself, watched her climax. He had climaxed too, right there in front of her, in full view, knowing she was watching. He had witnessed her throes of passion right in front of him. These weren't things siblings normally do. Mark thought maybe it'd be best to just put it behind them, and maybe the best way to do that would be to pretend like it never happened.

And yet he couldn't unsee it. Now whenever he saw her around the house with a loose-collared shirt hanging off her shoulders, he knew exactly what lay underneath. When she fed Emma, his mind superimposed the vision of her spread out on the bed, her body eager for stimulation.

If he was being honest with himself, he had started to see Kate differently even before he barged in on her; that's why he'd done it. Hearing her moans had gotten into his head. He'd only expected to get an eyeful of her and leave. He thought either he'd find it shameful and repulsive, or that the image of her naked would be enough to sustain him, at least for a while. And sure, he did find himself revisiting it when he was alone, but it didn't satisfy what he was labeling a curiosity. What would she feel like if he went further? How would he feel about himself?

He had gotten as far as he could on the meager diet of internet porn. He had tried the dating apps and came up empty. Nearly empty, anyway. Kate's profile was the only one on there in a fifty mile radius that held any appeal. Even with all the porn in the world at his fingertips, there was still a young, sexually active woman living in the same house with him. That was hard to ignore, even if it was Kate.

Growing up, he'd never seen her in a sexual way. For one, it would have been a complete non-starter. For another, she was a big girl and a late bloomer and not at all his type at the time. Since then, his tastes had broadened with his breadth of experience. And for her part, she didn't look like a frumpy, self-conscious teenager these days. She'd started working out. She'd grown into her curves. And then there was the obvious evidence that she was mature and fertile and sexually active, and that she'd actually had sex on occasion. That wasn't the Kate he knew before.

It was Saturday night, and after the baby's bedtime. Mark popped some popcorn and put on a movie. He and Kate settled down on the couch together, though at first Mark tried to keep a safe distance.

"You don't have to sit on the edge," she teased him.

"Fine," he said, scooting next to her, putting an arm around her shoulders.

This was how it had been when they were kids. Only now it wasn't so simple. She was in just a large, soft t-shirt and shorts. Feeling the heat of her next to him, it was starting to go to his head. He hoped in the dark living room, maybe she wouldn't notice.

But sitting so close side by side, he could see and feel the rise and fall of her chest. With every shift of his arm, there was a tremor in her, of expectation. Maybe they could get through this movie together without anything else happening, but they couldn't be normal together regardless. Not any time soon.

He let the arm around her fall so that his hand lay atop her breast, testing the waters. She put her hand on his, holding it there, but stopping short of anything more. He pressed his fingers into her soft flesh through the t-shirt fabric, and found her nipple stiff under the shirt. She gasped in a way he recognized as arousal.

"Don't start anything you can't finish," she said, without taking her eyes off the screen.

"Who says I can't?" he said, leaving his hand where it was.

"That's not what I meant."

She probably meant that it was a boundary they shouldn't cross, but she also hadn't exactly said that either. "I know what you meant. But you don't think I could? After all, I know what it takes. I know how you like to be touched."

"Hm," she gave him that begrudgingly. "I know what you're trying to do, and it's not going to work."

"I'm not trying to do anything. It was a complete hypothetical," he said. He knew it wasn't convincing, given his hard-on.

"In that case, I'm calling your bluff. Prove your hypothesis, then," she said, reaching into his lap. He gasped at her touch. "Is there a problem?"

"Fine," he said. With this line already crossed, he let his other hand start touching her belly. He couldn't believe they were doing this. Watching each other across the room was one thing. Touching each other was something else. And yet, he couldn't complain about her hand stroking him through his shorts. His whole body cried out for more.

He reached the waistband of her underwear. He could feel her pressing up against him, but he didn't want to do this clothed. He tugged on the hem. "You first."

She shook her head. "No, we both go, on the count of three. One, two, three."

They stripped from the waist down simultaneously, and then settled back down on the couch. They sat face to face so they could touch each other, one of her legs along the back of the couch, but they kept a safe distance between them.

As she reached for his cock, Mark reached down, finding her already soaking and hot. Maybe he wasn't the only one with this idea. He knew he had to prove himself, and so he tried to touch her the ways he'd seen her touch herself, and he paid attention to what provoked a reaction in her. The more she lost control to him, the harder she stroked and fondled him. Sometimes it was hard to concentrate on his goal.

She was quickly building up to her peak, when he dared to slip a finger inside her. This took her arousal to another level entirely. Her muscles clamped down on the invading finger, and a tremor rippled through her bulky frame.

"Kate, I'm about to..." he warned her.

"Me too," she replied in a strained voice.

That turned out to be an understatement. She screamed, her body convulsing. He felt the undulations of her muscles from inside her. He had never felt that with any other girl he'd been with, and it sent his mind reeling. His own sister was showing him what was possible.

Somehow through it all, she kept stroking him through her own climax, until he lost control. Despite the distance between them, his semen shot out, landing on her abdomen and lower, pouring down into her cleft, coating his fingers where she was still bucking against them.

When she felt it, she quickly got up off the couch, running on wobbly legs to the bathroom. "Shit shit shit shit shit," she hissed.

Mark wiped the rest of his semen off of himself, and cleaned up their fluids on the leather couch before following after her. In her haste, she hadn't bothered to close the bathroom door. She was standing at the sink, desperately trying to wash him off of her pussy. Out of her pussy.

"Are you okay?" Mark asked.

"No I am not okay," she said. "Exchanging bodily fluids was way, way over the line."

"Yeah I know," Mark said, he wasn't sure where the line was exactly anymore, but he knew that had been too much. "Sorry about that. That doesn't normally happen."

"I believe you," she said. It wasn't the first time he had ejaculated in her presence after all. "It'll be fine. I can handle it. This isn't the first pregnancy scare I've had."

Mark leaned against the doorframe, the full weight of what they'd done hitting him hard in the chest. That aspect hadn't occurred to him. "Yeah and look how that turned out." He gestured to where Emma was sleeping.

"I said I'll handle it," Kate said, clearly annoyed now

"Sorry," Mark said, and he left her to it, feeling awful in fresh ways about what they'd done. He hoped maybe if he slept it off, they could put it behind them in the morning. Maybe this feverish longing would go away, now that he'd satisfied his curiosity and killed the metaphorical cat.

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

Kate found herself going a bit mad. After that incident, she'd gone out and gotten a morning-after pill. It made her feel awful for a couple days. It wasn't the first time taking one, and she hated the experience every single time. But she wasn't prepared for the alternative.

When that faded, she had to admit that up until that moment where it all went wrong, it had been going pretty darn right. It had been the most contact she'd had in years, and definitely the most intense orgasm, by an order of magnitude. It had been a real shame to have to cut it short. She found herself fantasizing about how else that encounter could have played out.