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(Once in a) Blue Moon

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They're just fucking around. Derek let his eyes linger a little too long that one time Stiles was stripping out of his sweaty shirt after a training session and Stiles caught him. He grinned wickedly at Derek and showed up at the loft the next night smelling of desire and determination.

Derek tried to resist. Kind of. Okay, he didn't so much try as take one step back when Stiles walked right up to him, grinning and saying something along the lines of, "I know you want me." Derek's still not sure what exactly he said. He was distracted. Stiles was up in his business, quite literally backing him into a wall, and saying things and touching Derek's arm and it was... distracting.

The point is, they're just fucking around. Stiles comes home on the weekends, and they fuck. Derek visits him on campus sometimes, and they fuck. Occasionally, when they’re busy, they meet halfway and get in a quicky in the back of the Camaro, or the gas station bathroom, or that one time at Denny's. They don't really talk about it. Derek knows Stiles sleeps with people at school, he can smell them on him sometimes, and Stiles doesn't have any qualms about mentioning his sexual activities in front of him. It's enough that Derek knows Stiles isn't in this for anything more than sex, not that Derek wants it to be anything more. He hasn't been with anyone else but that's mostly because that might involve talking to people and he'd really rather not. He's satisfied enough with their fairly frequent encounters.

It's easier with Stiles, anyway. Stiles knows he's a werewolf, likes it even. He lets Derek get a little rough, toss him on the bed, hold him down a little harder than he'd be able to with anyone out of the know. Plus—and this is probably Derek's number one reason for loving sex with Stiles (beside the actual sex. With Stiles)—Stiles lets Derek knot him. Derek's pretty sure Stiles loves his knot, from the way he likes to reach back and touch the base when it's buried deep in him and there was that one time he said, "I really love your knot up my ass."

Like right now, Stiles is walking backwards toward Derek's bed, pulling the zipper of his jeans down, his shirt and belt already discarded. Not two minutes ago he stormed through the door to Derek's loft mumbling angrily about an essay and professors being asshats when he grabbed Derek and pulled him up the stairs saying, "I kinda need you to fuck me."

Derek didn't have to be told twice.

Derek pulls Stiles into a kiss by his belt loops before they reach the bed. Stiles puts his arms around Derek's shoulders and rubs his hands down his back to grab the hem of his shirt and yank it over his head. Derek kisses him again and Stiles sighs against his lips as his hands roam down Derek's chest and slink around to the small of his back so they're practically hugging. Derek takes some of his weight, letting Stiles relax against him and he maneuvers them onto the bed finally.

Stiles may have initiated but Derek takes charge now, knowing Stiles needs some stress relief—he looks worn, his body tight with stress and his eyes tired. Stiles lets him, more confirmation that he needs Derek to take the lead, to take care of him. Stiles always looks after everyone else, to his own detriment sometimes, and Derek knows how weary that can feel, knows it's nice to let go of the reigns occasionally and let someone else worry about the semantics. This is something he can do for Stiles, something he's actually good at.

Stiles goes pliant under him, letting Derek undress him fully. Derek pulls back to rid himself of his own clothes and when he looks down at Stiles—already looking more relaxed, loose limbs splayed across the bed and the tension in his features eased—something clenches in his chest. He's suddenly more grateful than ever that Stiles isn't a werewolf and can't hear the way his pulse is overreacting. Fucking hell. It’s just Stiles, and Stiles is—

—well, Stiles is gorgeous. Though he'd fight Derek on it if he said it out loud. He'd say, "Shut up, I'm adorable. There's a difference," like he still pictures himself as that gawky sixteen year old with a buzzed head and full cheeks. Not the lithe man he is now, with sharp bone structure and those lips. Christ, those lips. Derek captures them again, lining their bodies up and lowering himself slowly on top of him, feeling Stiles' body temperature and heart rate rise with the contact.

Stiles stiffens a little after a blissful minute of kissing and says, "oh," like he's just realized something.

Derek pulls back, concerned. "What is it? Are you okay? Did I do something?"

Stiles give him a look and rolls his eyes. "No, idiot. I just remembered the full moon is tonight."

"Oh," Derek says, eloquently (not really, at all). He relaxes, though. He's all too often worried he's doing something he shouldn't or being too rough or just ruining things in general. Force of habit, he supposes. “Right.”

Stiles laughs. “You’re a total loser. You’re a werewolf, and you forgot it’s the full moon?"

“I didn’t forget,” Derek huffs, leaning in again to kiss him. “There was one already this month.”

“And you didn't notice there was another.” Stiles looks impossibly amused, and he quirks one eyebrow, seeming to be waiting on something. “So...”

“So?” Derek asks.

Stiles keeps staring at him.

Oh," he says again, understanding. "You want me to?"

"Don't I always?"

"Yeah, but -"

"But nothing. Yes, okay? I want your knot." Stiles smirks. "Knot me up, buttercup."

Derek growls softly. "Shut up." Stiles knows he hates pet names.

Stiles has a glint in his eyes, barely holding a straight face, his lips ticking up at the corners when he says, "Aw, why so glum, sugarplum?"

Derek leans down and growls deeply against his throat so it reverberates through his skin. It doesn't have the affect he wants, though, because Stiles starts laughing. Typical. "If you really want to scare me into shutting up, you probably shouldn't get more wolfy.” He lowers his voice, grinning. “It just makes me want your knot more.”

"Maybe I won't give it to you," Derek warns, aiming for serious but falling somewhere closer to fond.

"You wouldn't," Stiles gapes, his eyes still crinkling with laughter. "You know you can't control it this close to the full moon."

It’s true. He can only knot a few days before and after the full moon and the urge is so strong, it’s difficult to have sex without it. He’s always avoided hookups near the full moon before, and it’s nice not to worry about it for once in his life. "Well, maybe I'll just fuck you with my fingers." He punctuates it by pressing two fingers against Stiles' hole and Stiles gasps, arching toward Derek.

"You're a knot-tease," Stiles says, looking down between them to Derek's dick, knot already beginning to swell at the base. Stiles pushes up and flips their positions, sitting back on his knees between Derek's legs. "Like you could resist me." He smirks and bends down to mouth at the bulge at the base of his cock.

"Shit," Derek wheezes. His knot is more sensitive than the rest of his dick and the metaphorical sparks start flying as Stiles works his lips up his dick and back down against his knot again, alternating between pressing with his tongue and sucking.

Stiles pulls back up, grinning. "Thought so."

"Now who's the tease?" Derek asks, breathing heavily.

"You started it,” he teases.

"Yeah, yeah. Whatever.” Derek rolls to the side and pulls some lube from the bedside table. He slicks his fingers and motions for Stiles to come closer. "Come here,” he says. Stiles straddles his legs and leans down to kiss him while Derek’s fingers brush underneath his balls and against his perineum and back.

Stiles groans into his mouth when he pushes two fingers in. Their kisses become sloppy and labored as he works Stiles open. Stiles’ arms are shaking with the effort to hold himself up and eventually he flops his chest against Derek’s, breaking the kiss to pant into Derek’s shoulder.

"Ready,” Stiles gasps. "Fuck, come on.”

Derek flips him and takes a moment to catch his own breath and slick his cock. He puts a pillow under Stiles hips and lines up. "You good?” he asks, looking Stiles in the eyes. Stiles rolls them.

"Yes, I’m ready. You aren’t going to hurt me, Derek. How many times do we have to do this?”

"Every time.” Derek fixes him with his stern face, which does absolutely nothing because of all the people Derek encounters on a regular basis, Stiles is the one who has seen him bared—in more ways than physically—and is immune to Derek’s bitch-faces.

He pushes in, stopping at the top of his knot, and gives a few shallow thrusts. Stiles pulls him by the shoulders and licks at his neck, his breath hitching with each thrust as he increases speed. "Do it already,” Stiles says, labored and sweating beneath him. They have this down to a science now, and he pushes in slowly, letting Stiles stretch and adjust until his knot is in completely.

"You good?” Derek asks again, his own breathing matching Stiles panting.

"Y-Ye,” Stiles stutters as Derek shifts, his knot pushing in further. "Yes,” he continues, "fuck. Yes, so good.”

Derek starts to move and Stiles bites at the base of his neck, moaning around the muscle, and Derek will never tell him that he’s the only person he’s ever allowed to do that. A lot of werewolves, especially alphas, would consider that a sign of submission. Derek thinks the idea is a little antiquated but it still makes the hairs on the back of his neck stand on end, the proverbial hackles. With Stiles, though, it’s not a warning—it’s nice, like a shiver down his spine.

Stiles wraps his legs around Derek’s waist, pulling him slightly deeper and Derek swears. "Shit. Stiles,” he huffs into his ear. He sucks on his earlobe and nips underneath at his jaw, his rhythm quickening.

Stiles gasps, "Your knot, I love it. Fuck, Derek...”

Derek hides his smile into the pillow beside Stiles head and reaches between them to grip Stiles’ cock. Stiles moans loudly and arches up. "Shit, mother fucking, hnng.” He stammers a few more nonsensical curses and comes when Derek slams in again, pushing so the pressure of his knot is against his rim.

Stiles head is thrown back on the pillow, his mouth open, panting and his neck glistening with sweat that Derek can’t resist. He gives his cock a few more tugs as Stiles rides it out then braces his hands on either side of Stiles’ head, ducking to kiss and lick at his neck, following Stiles’ adam’s apple as it bobs. He picks up his pace, using just a tad of his preternatural speed now that Stiles is more relaxed around him.

Stiles starts stroking his arms and runs his fingers down Derek’s sides, laughing when the muscles flinch. He knows Derek’s ticklish and if he wasn’t so focused at the moment he’d be squirming away. "Fucker,” Derek says, catching his mouth again. "Stop that.”

"I can’t help it. The big bad alpha’s ticklish.” Stiles smiles against his lips, laughing. "How I am supposed to resist that temptation? It’s too much. I’m only human, after all.”

"Shut up,” Derek sneers. He reaches down to Stiles cock to find he’s hardening again. He gives it a squeeze. "Do it again and no more orgasms.”

"Hey, no fair,” Stiles says, indignant, but it doesn’t really come across like he wants when it turns into a groan.

Stiles clenches around him, grinding down and he gasps, "Oh, fuck, Stiles.

"Yeah, come on.” Stiles bats his hand away and takes his own cock in hand, allowing Derek to focus on driving into him. Well, focus is a strong word, as Derek is more like a spastic faltering mess at the moment.

"You’re... you’re,” Derek mumbles under Stiles’ ear, nosing his hair, unable—and a little unwilling, if he’s being honest—to verbalize what’s going through his mind: amazing, tight, spectacular, unreal, everything, made for him. Then he’s coming, his knot swelling and pulsing inside of Stiles. He vaguely thinks he hears Stiles gasping and coming again but his head is clouded with pure pleasure and everything else is muted and faraway.

When the fog clears, he’s still trembling and Stiles is caressing his back, his legs splayed on the bed again for comfort. "Mmm,” is all he can say and he rubs his face against Stiles neck, breathing him in.

"Mmhmm,” Stiles replies, sounding just as spent. Derek shifts a little and they both groan when his knot pulls, sparking dulled aftershocks. They won’t come again—Derek’s still coming, actually, but it’s slowing now—but the after effects linger.

He pulls back to look at Stiles, his face is flushed and glistening with sweat, and he’s smiling up at Derek, looking satisfied and one hundred percent less stressed than he was when he first came in. "I’m what?” he asks, smirking.

It takes Derek a moment to realize what he’s referring to and then he has a moment of panic because he literally cannot run away from Stiles at the moment, his knot still pulsing dully in him, and he absolutely cannot say any of the things he was thinking. Stiles doesn’t want anything more from him and he’s okay with that. He doesn’t need anything from Stiles anyway. He’s fine with what they have. Sex is good. Sex with Stiles is more than good. It’s enough. Really.

Thankfully his knot has gone down so he quirks an eyebrow and, with his best cocksure attitude, he smirks and says, "You’re an asshole.” Then he pulls out as quickly and gently as he can to distract Stiles from his obvious avoidance.

Stiles lets out a laugh and moan mixture and stretches out gingerly when Derek plops on his back beside him. They lay together for a while, just breathing. Eventually Stiles sits up and heads to the bathroom. Derek watches him, eyes fixed on Stiles ass, on his flexing muscles. He can just barely see the shine of his come leaking down Stiles’ thigh and his dick twitches. He rolls onto his stomach and is starting to drift when Stiles comes back in.

"Dude, that was great,” he says, pulling his jeans back on, hopping around and looking for his shirt.

Derek grunts his agreement and Stiles leaves with a, "See ya,” hollered from the downstairs. Derek falls asleep trying not to think about how fucked he is.

...
...

Derek doesn’t see him again for a few weeks, until spring break. Stiles is busy with school and Derek’s been working on new training routines with Isaac and Boyd, and sometimes Scott. Scott attends the same college as Stiles just outside town and they usually come back together and do pack things. Not that Scott nor Stiles are officially pack. They help when needed and sometimes train together. Derek and Scott have come to a sort of truce, where they agree to disagree—on mostly everything—and they try not to lie to each other and withhold useful information. It helps to use Stiles as a mediator, otherwise they just end up yelling at each other for twenty minutes until one of them storms off.

They’re a work in progress.

He’s at the loft with Isaac and Boyd, going over the day’s routine. They’re all going to run the preserve and hit a few spots around town, just to make sure everything’s still good and clear. Things have been settled over the past year and Derek’s determined to keep it that way. Finally, the supernatural crazies have decided to give Beacon Hills a break. Derek likes to think it’s because he’s finally established his pack (kind of) and proved they can hold their own (mostly).

Scott and Stiles show up after a while and he’s stunned when he sees Stiles. He looks terrible. Derek knows he’s been stressed this semester—they text somewhat frequently—but his class load isn’t as bad as his last semester’s, he’s said so himself. This is more than the average college fatigue, that much is obvious. Stiles looks gaunt, with dark circles under his eyes and his face thinner than he’s ever seen it, his cheek bones poking out sharply, like they’ll slice right through the thin, pale skin.

Derek waits until Stiles goes to the kitchen by himself before he says anything. He follows silently and when Stiles is pulling a bottle of water from the fridge, Derek steps a little closer and says, keeping his voice low for privacy, "Are you okay?”

"Yeah, of course,” he lies. Derek just looks at him and raises his eyebrow a little. Stiles looks defeated and Derek absolutely hates it. He’d usually love getting Stiles to cow to him but not when he’s like this. This isn’t fun and games right now. "I don’t know,” he sighs, shifting on his feet. "I feel off. I’m exhausted but I can’t sleep well enough to feel rested in the morning and... I don’t know. It’s just stress.” He waves his hand dismissively, like he actually believes it as truth and not the load of crap it obviously is.

"Looks like more than stress. Have you seen a doctor?” Derek asks, taking a tentative step closer. He smells different too. It’s not strong, he only notices because he’s standing close enough to touch. He thinks about reaching his hand to touch Stiles’ shoulder but doesn’t, unsure if it would help. Stiles’ scent, though—he doesn’t smell sickly, exactly. Derek’s not really sure what it is but he knows it’s different and it’s got to be whatever's happening to him.

"No, it’s fine,” he dismisses again. He’s looking at Derek but his eyes keep shifting down to the bottle in his hands, his fingers picking at the label nervously. "It will be fine,” he corrects.

"I can,” Derek starts, unsure what he should say, or do. He feels like he should do something. He wants to comfort him, make whatever it is stop. Fix it. Break something. Anything to be useful for Stiles. "Uh, help?”

Stiles grins, brightening a little as his shoulders shake with a small laugh. "Wow. That’s so eloquent. Has anyone ever told you that you have a way with words, Romeo?” He waves his hand dismissively, still smiling. “I’m fine. Don’t worry about it. The semester will be over in a few weeks, I’ll come home, sleep for a week and be fit as a fiddle.”

"Okay, just. Let me know if you need anything,” Derek tries to look comforting but he’s pretty sure he just looks pinched. Or constipated.

Stiles steps into his space, ducking his head and playing shy while his body is crowding Derek against the counter. He smiles, coy. "I need to fuck you. How about that?”

Derek’s reaction is cut off when his brain registers what his ears pick up. Stiles’ heart rate sped up as he advanced on Derek, his arousal spiking too but there was something else. There, it happened again.

Oh.

Oh.

Oh fuck.

Another heart rate, quicker than Stiles but definitely coming from him.

Derek completely freezes and Stiles steps back, noticing the sudden change, his brow drawn in concern. "Derek? What is it?”

Fuck. "Uh...” is literally the only sound he can force out of his constricted throat. Holy fuck.

The rest of the guys appear from across the kitchen island. "Derek?" Isaac asks, looking as concerned as Stiles. Stiles glances between them and Derek, looking a little panicked, and a little guilty, like he did something he didn’t realize. No, actually, Derek was the one who did something without meaning to. Biggest understatement of the century. Jesus.

"What's wrong?" Boyd asks next. "Your heart is off the charts. What's going on?"

"Uh…" he looks between them all, still frozen in place. He can't make his body function. His brain is offline. This isn't happening. He can't… how is he supposed to deal with this? He can't. So he does the only thing he can do. He flees.

He’s already out of the apartment and down the hall to the staircase leading to the lobby when Stiles yells after him, "Where the fuck are you going?"

...
...

"So, you want to tell me why Scott can hear two heartbeats coming from me?”

Derek stops, spoonful of cereal frozen mid-air, and turns to look at Stiles, who just stormed through his door three days after Derek’s tiny meltdown. To say he looks angry is an understatement. He’s still unwell, like the other day, but his eyes are frantic and his face is flushed like he just ran up the three flights of stairs instead of taking the elevator. His heart rate is... well, no. Derek’s not going to listen to that right now. Nope.

"Well?” Stiles insists again. "This is what freaked you out the other day, isn’t it?” Derek places his spoon down and leans back in his chair, suddenly not so hungry for cheerios. "I swear to god, Derek, if you don’t fucking answer me right now, I will throw all of your leather jackets in a wood chipper."

Derek starts to raise his eyebrow but stops when Stiles points at him—emphatically—and simply says, "Don’t.” Then he pauses. "Answer the question.”

Derek sighs. "Yes.”

Stiles deflates like a balloon that’s been popped, letting out a ragged breath, like Derek just confirmed his death sentence. Which, he supposes he has, in a way. He closes his eyes and takes five deep breaths, and Derek’s worried he’s going to collapse when he starts to sway a little. But then he straightens, pulling his shoulders back. Stiles locks eyes with him and, oh yeah, he’s angry. Really angry. "This is bullshit!"

Derek’s not sure what to say, not sure he could actually say anything to make this better or to even explain it. "I’m sorry,” he offers.

"You’re sorry?” Stiles scoffs, pulling back a little with wide eyes. "You damn well better be.” He runs his hands through his hair and yanks on the ends, making it stick out crazily. "Are you fucking kidding me right now? This isn’t even possible! How does this even... I mean. What. The. Fuck.”

"I don’t know.” Derek knows he’s not being helpful but he honestly isn’t sure what else to say. This sort of thing isn’t supposed to happen. He’s never heard of anything like this.

"That’s it?” Stiles says, incredulous. "That’s all you have to say?”

"I don’t know, Stiles. It's not supposed to be possible.”

Stiles walks over to the dining table and sits across from him. He doesn’t reek of anger so much as resignation now. "Is there any other explanation? Maybe... I don’t know. Could I have turned into a Time Lord?”

"A what?” Derek asks.

"Doctor Who. Netflix, Derek, we’ve talked about this.” Stiles shakes his head, putting it into his hands. "Just. Anything else. Please.”

"I don’t know what to tell you.” He’s trying to sound comforting but he knows he’s not. Nothing about this is comforting.

Stiles looks up, angry again, like he’s just thought of something sour. "You didn’t...” He stops to take a breath. "You didn’t know, did you?”

"Jesus, Stiles. No.” He moves to reach for Stiles, to reassure him, but Stiles flinches, sitting back in the chair and out of Derek’s reach. Derek really can’t fault him for that, though. "I mean, knotting-” Stiles jerks narrowing eyes to Derek at the word, "-is about breeding but not between males. I didn’t think-”

Stiles looks startled, and pushes back from the table. "What? Tell me you didn’t know it was a possibility,” he demands.

"It's not a possibility!" Derek all but shouts. He knows he's in no place to be angry with Stiles but he's frustrated. Things were finally starting to go well for him, for the pack, and now he's gone and fucked it up again. Literally. "At least it shouldn't be," he adds, sounding defeated, which he is.

Stiles hunches over and bangs his head against the table with a drawn out exasperated, "Ugh." After a few silent minutes, Stiles says, with his head now pillowed in his arms, "Okay, is there anyone we can talk to about this who might be remotely helpful?"

"Deaton?" Derek suggests.

"I said 'helpful', not 'cryptic'."

"I don-"

"Say 'I don't know' one more time, Derek, and I swear to god I'll go straight to the hardware store and buy that nice, shiny wood chipper," Stiles says, sitting up just to move his head into his hands, resting his elbows on the table. Derek's never seen him look so exhausted.

"I’ll figure it out,” Derek says, aiming for reassuring. It doesn’t work. "I can... There’s a few contacts I can try for information.”

"Yeah?" Stiles lifts his head up, finally looking him in the eyes. Derek nods. "Find out how to make it go away.”

Derek stares at him. He did expect. But no, of course Stiles wouldn’t want. He doesn’t even want. Jesus, this is all too much. He’s barely got a functioning pack. He’s barely functioning himself. How are they supposed to raise a... "Right,” he says with a curt nod. "Of course.”

Stiles’ brows are drawn and he’s looking at Derek curiously. "You don’t want... I mean, you know this is insane, right? You can’t possibly want me to have your baby, can you?”

"No,” Derek says a little too quickly. "I mean. Fuck, I don’t know, Stiles. It’s a pack thing.”

Stiles’ eyebrows go up. He’s angry again. "So I’m supposed to have your little wolf cub out of pack loyalty? Is that honestly what you’re going with?”

"No! I’m not saying that.” He’s really messing this up worse than he already has. "You can do whatever you want.”

"Fuck yes, I can,” Stiles interjects.

"I was surprised, is all. There’s a lot of instinct that comes with pack and I... nevermind.” He’s not sure he can explain it to Stiles. His own packmates might not even understand the instinct to cultivate a pack. They’re not Alphas. He sighs. "Forget what I said. I’m sorry about all of this, honestly. I’ll find out whatever I can and I’ll ask about that.”

Stiles watches him for a moment before speaking. "Thank you.” He must see something in Derek’s face because he adds, "Listen Derek, I get that this could be a big deal for you because of werewolf... things, but you’ve got to understand where I’m coming from.”

"I do, I swear. I would never ask you to do something like this.” He leaves off the for me.

...
...

There's a pack a couple of hours north of Beacon Hills: the Harrison pack. They were, for lack of a better word, allies with his family. Both peaceful packs that mostly kept to their own vast woodlands. When his family was killed, the Harrison’s had offered he and Laura a sanctuary, to be their own sub-pack of theirs, so to speak. It was a nice idea, to have a safe place to grieve, to get their heads on straight and a place where Laura could learn about being an alpha. They considered it briefly but ultimately decided to get as far away from home as possible. He wishes now they had gone, for even a little while.

There’s so much he doesn’t know about being an alpha, or hell, even about his own kind.

It's probably not the best idea—not that he ever has ideas that could be referred to as 'best’—but he decides to contact them. Their alpha, Sherice, was older than his mother but he remembers her as warm and friendly from the few times their families connected. He calls the number scrawled down in Laura’s old journal.

After the fire, she took to writing down everything they knew—names, locations and numbers of other packs, account numbers, birthdays, anything they might need to know. Their mother had an incredible memory, she never forgot a birthday or anniversary and always sent a card. They wanted to preserve that.

Derek has looked at the journal a total of once since he returned to Beach Hills. He found it with Laura’s things, at the old house, and the last entry was some of the facts she’d learned about the fire, the research that led her to her death. He’s finally picked it up again after his conversation with Stiles.

It’s his responsibility to find some answers for Stiles and it’s the only place he can think to start.

He calls the number listed in the journal and has to talk to three people before he gets Sherice on the phone. He apologizes for the bother and explains the situation.

The line is silent for a bloated twenty seconds before she sighs, "Oh honey, what a mess you’ve made.”

Story of his life.

"Have you ever heard of this before?” he asks. He’s pacing in front of the large windows of the loft. The sun’s shining on him and he wishes the windows weren’t so big, so he could blot out the stupid bright sun with curtains.

"There are stories. It’s incredibly rare but there have been a few instances, I believe. Not in many years, though.” Her voice reeks of sympathy and Derek’s pinching the bridge of his nose so hard he thinks he might be giving himself a headache. "Several things have to be in alignment for it to occur.”

Fuck his life. Seriously. "Such as?”

"I’m not an expert but from what I understand, for conception to take place within a male, the mating has to happen on a blue moon and your mate would have to be a mage.”

He’s not sure he can process that; so many of those words are breaking his brain. Conception. Mate. Mage. Mate. Jesus H. Christ. Stiles isn’t his mate. They’re just... they don’t. They’re just fucking around. Stiles doesn’t even like him. Okay, that’s not entirely true but not the sort of like—affection, whatever—mates would have.

"Derek?” Sherice says over the line.

He comes back to himself. "Uh. Yeah, thank you.”

"Last month,” she says, like it’s supposed to mean something, and when he doesn’t say anything she continues. "The blue moon?”

"Oh.” He’s not doing a very good job of sounding like a competent alpha at the moment. He forces himself to sit down on the couch and focus on the conversation. "Right, yes. That’s when we...” He sighs. "I didn’t know it was even possible,” he says, mostly to himself.

She doesn’t say anything for a moment and when she does, she sounds so much like his mother when she comforted him as a child. Sincere and comforting and fiercely protective. He always felt so safe with her. He hasn’t felt that way in a long time. "Honey, how would you have.” It’s not a question.

"Um, he,” he clears his throat at the thought, "doesn’t look well. Is it safe for him?”

"His magic should allow it and protect his physical body.”

"I’m not sure he knows he’s a mage.” There were a few times, back when he was in high school, when Stiles used mountain ash successfully but Derek’s not aware of Stiles practicing.

"Oh. That could present a problem,” says Sherice, and Derek really doesn’t like the way this conversation has gone at all.

...
...

Derek is restless so he decides to run to Stiles’ house instead of drive. He needs to burn off some of this nervous energy. He’s not looking forward to telling Stiles about his conversation with Sherice. He already knows Stiles isn’t going to like what she had to say.

The sun is just setting as he reaches the Stilinski house and Stiles’ Jeep is alone in the driveway. Derek’s never been more glad to see the Sheriff isn’t home. This is not news he’s looking forward to sharing with him. Congratulations, I knocked up your son!

Stiles calls for him to come in when he knocks on the front door. He finds Stiles sitting at the kitchen table, staring morosely at a plate of eggs. He doesn’t look any better. If anything, he looks worse.

“What’s wrong?” Derek asks. Stiles glares at him. “Uh, morning sickness?” he offers.

“Har har.” Stiles does not think it’s funny. “I want to eat them. I make excellent fried eggs, Derek.”

“So eat them?” Stiles glares again. “Or don’t?” He’s sure there’s nothing he can say that will help but he thinks he’s supposed to try.

“It’s like, I don’t feel hungry but I know I have to eat because if I don’t, I’ll feel sick. But I don’t actually want to eat them, even though I do.”

Derek’s not sure what to say to that so he doesn’t say anything at all. He sits across from Stiles and watches him sigh and grumble to himself as he picks at the eggs, taking small, cautious bites. He looks physically pained, eating them.

“What’d you find out?” Stiles asks around a bite.

Derek steels himself, because since their conversation, he’s been trying to figure out how to tell Stiles what he’d gathered from Sherice without freaking him out. He’s already decided that option definitely doesn’t include him mentioning how they’re apparently mates. He hesitates. “The reason you’re...” He can’t bring himself to say ‘pregnant’. He just can’t. The look Stiles gives him suggests that he knows exactly what he is, anyway. “There was a... confluence of events.”

“Now is not the time to be cagey,” Stiles says, fixing him with a hard look.

Derek winces, and nods. It’s better just to get this over with. “Last month, there were two full moons, remember?”

“The blue moon,” Stiles says, shaking his head. “I was even talking to Scott about that the day before. I wondered what it was like for you guys. If you felt the shift like any other full moon or if it was different. I should’ve fucking known.”

“It’s not just that,” Derek continues. “It was the blue moon, combined with what we are.”

“Really fucking stupid?” Stiles supplies. “Or, one of us is.”

Derek ignores that, mostly because he agrees. “I’m the Alpha”—Stiles rolls his eyes—“and you’re a mage.”

Stiles’ head pops up, eyes locking on Derek’s with an intensity that has Derek’s chest clenching. “A mage? As in magic? I’m magic?”

“I thought you already knew that,” Derek says. “I thought Deaton... with the mountain ash?”

“Deaton said I could be a ‘spark’, whatever the fuck that means. Sifting some ash around doesn’t mean I’m magic. It didn’t feel like anything other than an adrenaline rush. I mean, I’m not... I don’t see how.” He pushes his plate away and puts his head in his hands with an exhausted groan. Derek hates the sound.

“I don’t know what being magic is supposed to feel like,” Derek says cautiously, fingers itching to reach out and touch Stiles and comfort him in some way. He puts his hands under the table instead.

“That’s because you don’t know anything,” Stiles mutters into his hands, and Derek sighs, but carries on.

“But because everything came together that night, that’s why you’re... You know.”

“Trust me, I know,” Stiles sighs, dropping his hands onto the table to look at Derek. He looks like he’s been run ragged—there are circles around his eyes now that Derek’s looking closer, and it’s the first time that Derek can remember him not teeming with energy. All of that worries him.

“It’s protected,” Derek says, watching Stiles’ eyebrows rise up in confusion.

“Try that again in human terms, wolf boy.”

“It’s protected,” Derek says again, slower, hoping that Stiles can understand what he’s saying without him having to spell it out. It seems he’s out of luck on that front. “You shouldn’t be pregnant—” there, he said it "—but you are, because of your magic and because of mine. The two combined are what makes it possible at all.” He pauses, hating that he has to say it, that he can’t give Stiles what he wants. “And it makes it impossible to stop it.”

“Stop it?”

“It’s the first born of an Alpha.” Derek wants to shrivel up and die. “Werewolves have a lot of powerful magic, even if we can’t consciously use it, like you. That magic is protecting the baby—” he can’t help the way he whispers the word “—until birth, then it comes under the protection of the Alpha and pack.”

“Are you kidding?” He doesn’t look mad but Derek can feel the anger beginning to vibrate off him.

“No,” Derek says, shaking his head and staring at a knick in the table. He can’t look Stiles in the eye anymore. “I’m sorry, Stiles.”

“And I’m supposed to just go along with this?” He sounds angry now. “I don’t get a choice? What’s done is done and that’s it?”

Derek doesn’t know how to answer that, so he keeps his eyes downcast.

“That’s not good enough,” Stiles snaps. “If we’re both ‘magic’, there’s got to be some way to reverse this. If your contacts know how this happened, they must know a way to reverse it.”

“It’s old magic,” Derek says, quietly. “If there was ever a reversal, and I’m not saying there was, it was forgotten a few hundred years ago, Stiles.” He makes a frustrated noise in the back of his throat. “Most Alphas would have known about the blue moon and wouldn’t have done it unless they were... sure.”

“But you didn’t know,” Stiles says, flatly. He laughs, and Derek’s head snaps up to look at him at the sound. Stiles looks close to having a full on panic attack. “Because you’re the worst fucking Alpha ever. Jesus. This isn’t happening.” He laughs again, hiccuping on the noise. “I’m graduating next year, I’m not having a were-baby. This just, no. No.”

“Stiles,” Derek says, reaching out to put his hand on his arm but Stiles pulls back, sharply.

“Don’t,” his voice is rough, tinged with panic. “I... uh—” he swallows and clears his throat, breath too quick, “—you should leave now.”

“We can figure this out.” He wants to reassure Stiles but he knows it’s not something he can promise. “We can—”

“Just go, Derek.” Stiles is still vibrating with an angry energy but his voice has gone soft and too quiet.

Derek lets out a shaky breath and nods. He rises but stays there for another moment, reaching for anything else he can say to make this a little less worse for Stiles, even though he knows there’s nothing. “I’m sorry,” he says again, and he does as Stiles asks and leaves.