Everything started with Derek's strange pillow talk. They were curled up together, still coming down from their orgasms when Derek mumbled something into Stiles' neck that he didn't quite know how to respond to.

"I wish I could breed you."

"...What?" Stiles asked, convinced he had misheard.

"I want to fill you with my pups, want to run my fingers over you swollen belly," Derek mumbled.

Stiles didn't know what to say exactly. He knew it must have been a werewolf thing, and, really, it wasn't all that strange. Derek's knot was still inside of him, slowly deflating. A few words was nothing in comparison to that revelation.

*

The next day, Stiles mulled what Derek had said over in his brain in class. He was pretty sure he couldn't get pregnant, that wasn't a werewolf thing, no matter what the internet would have him believe. Derek would have warned him. Someone would have warned him. What Derek said in the heat of the moment (or just after it) had no bearing on something like that.

Scott started making faces at him from the other side of the room and Stiles put the idea out of his head.

As soon as his dad went to work, Derek slipped in his window. Stiles suspected that his father had worked out what was going on with him and Derek; Scott had let a few too many things slip in front of him and Stiles' father wasn't a stupid man. Still, he was pretty sure he wouldn't be okay with what they'd been doing in the house. A long time ago, he'd given him the talk and the one thing Stiles could remember through the embarrassing memory was that he wasn't allowed girls over. He assumed he'd feel the same about Derek.

So, Derek would slip in at night and out again first thing in the morning. Stiles hated that his bed was empty when he woke up but it was the best they could do for now. Sometimes Scott would let him pretend to be staying at his and Stiles would stay with Derek but they could only really do that when he didn't have school in the morning.

"You can use the door, you know. My dad's long gone," Stiles said.

"That would just take more time," Derek said, walking across the room and pulling Stiles into a kiss.

He always got like this when he first arrived, or when he met Stiles anywhere, no matter who was around.

Stiles had asked him about it once when they were lying in bed and Derek had looked away for a second, surprisingly embarrassed, then he'd mumbled something about not liking it when Stiles smelled like other people.

Apparently just brushing shoulders with people in the school corridor made him smell quite different to a werewolf.

Derek's hands roamed all over him as he kissed him hard. Stiles raised his arms to let Derek tug his t shirt off over his head.

The two of them fell back onto the bed, Stiles groaning when Derek ran his tongue down his chest.

"Missed you today," Stiles said.

"Mmmf," Derek mumbled as he kissed his way down his body.

Derek didn't say much during sex. He didn't say much ever, but he really didn't during sex. He liked to focus and use his mouth for other things, whilst Stiles usually couldn't stop talking.

The words he did say, though, always did weird, unexplainable things to Stiles.

He never thought he'd like feeling owned by someone, but he did. He liked feeling the marks Derek left behind under his clothes the next day (or next week) and he liked the way Derek told him that he was his.

Derek's hands slid down to the hem of his own t shirt and he pulled it off over his head. His muscles flexed with the movement as the fabric moved up over his chest. Stiles licked his lips, staring at the way Derek's fingers moved over the button of his jeans, popping it open before unzipping them. Derek kicked his jeans off of the bed. Stiles had stopped being surprised about his lack of underwear. It was Derek, nothing surprised him any more.

His cock was hard, jutting up against his stomach, but Stiles didn't get much time to take it in. Derek bent back down onto the bed, placing his hands either side of Stiles' shoulders and pressing their bodies together.

Stiles moaned softly when Derek pressed his mouth and nose into his neck, inhaling deeply. His teeth ran over his neck carefully, he was always gentle with his teeth but Stiles had seen the effort that took in his eyes and the way that his muscles trembled.

Stiles wished he didn't have to be so careful. That was pretty much the only thing he hated about being human. He wished Derek didn't have to hold back with him, he wished that he could bite him and be as rough as he wanted. Instead, Derek was surprisingly soft with him; the preparation he'd insisted on the first time they'd slept together had almost driven Stiles mad.

Derek's finger eventually found their way to the waistband of Stiles' jeans. He unzipped them and yanked them off quickly, following with his underwear.

The cool night air felt good on his skin and Stiles couldn't help groaning when Derek ran his fingers over his cock.

"It's always straight to the sex with you, isn't it? You barely even say hello," Stiles said. "Actually, wait, did you even say hello?"

"Do you want me to stop?" Derek growled.

Stiles laughed.

"Don't you dare."

Derek's skin was hot against his, he was always so hot, practically burning when they were fucking.

Stiles reached up and pulled him closer, kissing him slowly as Derek fumbled blindly in his bedside drawer for the lubricant.

He didn't waste time but Stiles wouldn't actually complain. When they had first started... whatever this was... Derek had barely touched him. Aside from pushing him up against walls and using him to lean on, Derek kept his hands to himself, afraid that he was going to hurt Stiles.

This was much better.

Derek kept kissing him as he slipped his lubed up fingers against his hole, circling lightly before pressing one into him slowly. Stiles felt his cock harden further, twitching as Derek curled one finger inside of him.

It had hurt the first time but he was used to the feeling. Once he'd gotten used to Derek's knot, this was nothing.

Derek slipped another finger in as his other hand closed around his cock, drawing a deep groan from Stiles.

He'd seen him the night before, but it felt like he'd been waiting for ages.

"Please... I'm ready..." he said but Derek shook his head.

Even now he was cautious. He knew Stiles couldn't heal and he refused to do anything that could actually hurt him. For too long.

A third finger made him gasp and buck his hips involuntarily. Derek laughed but then he pulled his fingers out slowly and gripped Stiles' hips.

He flipped him over effortlessly. Stiles pushed himself up onto his hands and knees as Derek applied lube to his cock. Stiles braced himself; breathing deeply as he felt Derek line up against him.

Derek's nose brushed against his spine as he pushed into him, fingers pressing lightly into his hips. They still ached from the night before, Stiles could almost always feel where Derek's fingers had been.

"C'mon, fuck me," Stiles said as Derek slid into him slowly.

It was always agonising at first, before Derek began to move faster, thrust harder. There was always a point at which he lost control a little, when Stiles felt his claws digging into him, when his voice got harsher.

That was when Stiles liked it, when Derek fucked him hard and his knot started to stretch inside of him.

It didn't take Derek as long any more, he let himself go more readily. He pressed soft kisses to Stiles' spine as he thrust into him, one of his hands slipping around his waist to stroke his cock slowly.

Stiles moaned loudly, forever grateful that he didn't have any close neighbours. Derek's hips snapped forward, slamming into him. Stiles heard a deep growl. It vibrated through him, straight through his bones.

The bed was knocking into the wall with each thrust, a steady rhythm that beat in turn with Stiles' heart. He pushed back, shifting his hips to try to get Derek to push deeper into him. He could already feel the stretch, the slight burning sensation that throbbed through him as Derek's knot formed.

Stiles clenched his teeth, forcing himself to relax as Derek's fingers dug into him. His thrusts became harder but shorter as his knot slipped further into Stiles. Derek's breathing was ragged as he pulled Stiles back onto him and, with one hard thrust, he pushed all of the way in, locking them together.

Stiles groaned, stars exploding behind his eyes as the knot pressed against his prostate. Derek's hand squeezed his cock harder, stroking him fast. Stiles panted, pushing his hips back into Derek's as he came hard, his muscles clenching and trying to close around his knot.

"Fuck, fuck, fuck," he breathed.

Derek's face was pressed into his back, his hands holding him still. Stiles could feel him coming, his cock pulsing into him. He wondered what that felt like for him. Derek didn't just come and then it was over. His knot locked them together for at least twenty minutes and his cock kept emptying into him for around half of that time. It slowed down towards the end, from the feeling of it, but Stiles wondered if it felt like a full orgasm the whole time or just for the start.

Derek gave no indication through it, he just held Stiles close and still, breathing hard, his hips twitching occasionally.

After a few minutes, when Stiles' heart had finally slowed to a normal pace and he could think straight again, he noticed that Derek's hands had drifted slightly. His left had moved up and was brushing comfortingly against his back and his right had moved around his waist. His thumb was rubbing small circles on his stomach and Stiles was reminded of what he'd said the night before.

He ran his own hand over his stomach and paused. He was shocked to feel a slight swelling there. His stomach was firmer than usual, not giving when he pressed his fingers into his flesh. Derek was still coming, he could feel it, but it had slowed down. Stiles had never really thought about the sheer volume of it, but it must have been a lot.

Derek's hand brushed over his stomach, fingers pressing lightly. Stiles had never noticed the bloated feeling before, but then again, there was always a lot going on with his body after sex.

A low growl emanated from Derek as his fingers pinched at his stomach. Stiles shuddered as he felt the pressure increase a little when Derek's cock twitched inside of him.

Within a few minutes, his knot started to deflate and Stiles felt his come start to drip down his legs. Derek's fingers ran up his legs, pushing it back up and trying to hold it in as he pulled his cock out.

Stiles dropped his shoulders onto the bed, angling himself to stop it from leaking out onto the bed. He was surprised at the way Derek had touched him, the tenderness had sent a thrill through his body.

Derek pressed his face into Stiles' ass, flicking his tongue out and circling it around the ring of muscle. Stiles shuddered, feeling Derek's fingers running over his body.

One of his hands paused at his hip, snaking around to his stomach again, running slowly over his skin.

Stiles had an idea.

He pushed himself up slightly, making sure he didn't move too much. He reached slowly over to the still open draw and felt around inside until his hand closed around something cool and hard. He pulled out the small blue butt plug that he'd bought when him and Derek had first gotten together.

Derek had spoken to him before they slept together and suggested that he do something to prepare himself for the knot. The toy had been the best thing he could think of. He wore it on and off for a week before their first time, hoping that would help. It could have helped more.

Stiles passed the toy back to Derek.

"What..?" Derek asked.

"Trust me, just put it in."

Derek did so, holding Stiles open with one hand and pushing the plug in with another. After the sex, it slipped in easily, locking Derek's come inside of him.

Stiles straightened up, now that he didn't have to worry and turned around to see realisation dawn on Derek's face.

"Oh..." he said quietly.

There was something else in his expression and it took a while for Stiles to register it as a little bit of shame. He hadn't seen anything resembling that on his face before.

"Do you think I'm a freak?" he asked.

Stiles shook his head. It was pretty weird. But he'd grown up with Scott... and the internet. He'd heard and seen worse.

"I want you to fuck me again," Stiles said.

Derek's eyes widened but Stiles knew it wasn't going to be difficult for him. Sometimes they would curl up together, naked and sated and then minutes later, Derek would be hard again. They'd never fucked twice in a row, though, not without a little rest in between.

Derek might have werewolf stamina, but Stiles didn't.

He ached a little, his hips bruised from Derek's touch but he thought he could go again. Or he could at least handle Derek fucking him again.

He crawled forwards, wincing as the plug shifted inside of him. He kissed Derek softly, before biting his lip and sucking it into his mouth. It took three tries, but eventually Stiles got Derek to lay on his back so that he could crawl on top of him. They kissed, less heated than earlier, as Stiles felt his cock start to harden slowly. He relaxed his arms, lowering himself onto Derek's body, gasping at the increase in pressure as his stomach pressed against him. Derek was hard already, smearing pre come onto their skin.

"You're so perfect," he muttered into Stiles' neck, kissing and licking, sucking a dark bruise.

Stiles shook his head, unable to deal with Derek complimenting him, even in vague ways like that.

"How do you want me?" Stiles asked, grinning.

"On... your back," Derek replied.

It surprised Stiles, he'd always been on his knees. He would appreciate not having to hold himself up, but they'd never been face to face before.

That would be interesting.

Stiles rolled off of Derek, scrambling up towards the pillows. He spread his legs as Derek crawled up towards him, eyes dropping down to the plug sticking out of him. He reached down and tugged on it lightly. Stiles relaxed as it slipped out of him.

Derek picked up the tube of lubricant and squeezed some out onto his palm. He ran it over his cock but didn't bother using any more on Stiles. He really wasn't going to need it.

Derek kissed him, eyes meeting as he began to press into him for a second time. Stiles saw his eyes flutter closed as he moved; he'd always imagined Derek's face looking the same as it usually did, stern and unmoving. He looked strange with his eyes closed.

Stiles gasped as Derek thrust in faster, his cock twitching and getting slightly harder.

"God, Stiles, I didn't even need to lube you up..." Derek breathed as he slid out and thrust back into him.

By the time Derek's eyes started to flash, Stiles was fully hard again, biting his lip as he ran his eyes over Derek's body. He liked being able to see him.

Derek's rhythm began to become uneven as his teeth lengthened, glinting in the moonlight streaming through Stiles' window.

It took longer the second time, but within a few minutes, Derek's knot began to form again. It swelled inside of Stiles as Derek's hands pulled at him, forcing him to meet his thrusts. They locked together, causing Stiles' cock to twitch madly.

Derek's head dropped down, tongue flicking over his nipple, lips closing around it and sucking gently. Stiles groaned and bucked his hips, coming over his stomach. Well that was new.

Derek smiled, grunting as his body rocked against Stiles, rutting desperately as he started to come again. Stiles could feel it, pulsing, pumping into him.

Derek's hand was back at his stomach, rubbing gently. Stiles slipped his hand down, feeling his skin as Derek came. It was definitely doing something. He could feel the bulge growing under his hand, his abdomen swelling as Derek's cock pulsed inside of him.

A few moments later and he started to feel stretched, beyond bloated, like there was no more space inside him, but it didn't stop.

Derek whined against his neck, his hands just holding his stomach as he continued to fill him up.

"Mmf, Derek, there's no more room, stop," Stiles groaned.

"No, gotta fill you up. Not enough yet."

It slowed down, but Stiles could still feel the steady throb inside of him. He took a breath, not too deep because that only made the pressure worse.

After a few moments he twisted one of his hands in his sheets, trying to focus on the feeling of Derek's cock inside of him. He was pretty he had stopped coming, but his knot was still hard inside of him.

Stiles looked up at Derek, amazed at the wild look in his eyes. He'd never seen him like that before.

He looked genuinely disappointed when his knot started to deflate. It didn't so much leak out this time, it was more like a rush as Derek pulled out. Stiles clenched quickly, stopping as much as possible. He ran his hand over his stomach, amazed at how much he had inside of him. He could see a curve to his abdomen in the low light. It definitely wasn't in his head.

He relaxed his muscles, sighing as the pressure lifted. It was weird, really weird and the sensation was something he'd have to get used to. Maybe it was something to do with the way Derek looked at him, but Stiles couldn't help wondering if he could take another round.