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Derek knows Stiles is his mate when Stiles is a baby, is still Genim, swaddled against Claudia's chest in a bundle of cloth. Derek is at the library, by himself because he's seven and that means he's mature. He's half-way through the children's shelves when he smells it. Warmth, and home, and sweet honey on a summer's day. There's baby smells, too, but Derek's used to those. Then there's the familiar smell of Mrs. Stilinski, the librarian. Derek loves Mrs. Stilinski. She's nice and smells like apple pie. She's married to the Sheriff, who plays pool with his dad.
Derek follows the baby-honey-home smell and finds Mrs. Stilinski sitting behind her desk with a baby curled up against her chest, wrapped in a blanket that smells old and worn. There's a younger woman standing beside Mrs. Stilinski and between cooing at the baby and looking tired, Mrs. Stilinski shows the woman how to check out books.
Derek walks up, peers over the counter with both hands gripping the wood. "Hiya, Mrs. S."
She looks up, smiling. "Hello, Derek." Derek stares at the baby. It has a little bald head and is looking around with huge amber eyes. Mrs. S giggles, "This is Genim."
The baby lolls it's head to stare at Derek. It gurgles and gives him a gummy smile. Derek waves, "He's pretty."
The young woman laughs, "He's a boy, silly. He's not pretty, he's handsome."
Derek glares at her. He thinks pretty is a better word. He shakes his head, "He's pretty."
"Thank you, Derek." Mrs. S says with a smile, "Maybe you and Genim can be friends. You'd look out for my little boy, wouldn't you?"
Derek nods, because that sounds like a responsibility and he's mature and can handle responsibilities.
"Well, I'll make sure Genim knows you'll watch out for him, okay?" Mrs. S says. Derek smiles. He really loves Mrs. S. He doesn't like the young woman, because she shoos him away and says that new mothers don't need to be hassled. Derek goes home with the baby-honey-home smell in his nose.
--
Laura tells him he's a sap. But, she's twelve and stupid, so he doesn't listen. He sits on the counter and tells his Mom all about how Mrs. S thinks that he can take care of Genim. Laura makes fun of the baby's name. Derek sticks his tongue out at her because he likes it.
"It's a Polish name, Laura." Their mother says, waves a spoon covered in spaghetti sauce. "I think John's father was named Genim. Claudia was talking about it just before the baby was born."
"It's still funny." Laura mutters and swings her feet. Derek hates it when she swings her feet because it means she'll try and kick him.
"I like it." Derek says firmly. Then he looks at his Mom, "Genim smells nice. Much better than Uncle Peter and Aunt Joyce's babies."
"Oh?" She asks, and she's got her Alpha-I-know-everything voice on.
"Yes." Derek tells her, "He smells like honey and warm and home."
"Isn't that something?" She murmurs, takes a sip of the sauce and reaches for the pepper.
Derek's about to ask her what that means but then the gravel outside is crunching and that means his dad is home. He and Laura jump on him while Uncle Peter walks down the porch steps with one twin on his hip and one cradled against his neck. They're two and smell like peanut butter and candy. Derek doesn't like the combination.
"Hey, kiddos!" Their dad croons, scoops Derek up and swings him around. Laura, because she says she older and sophisticated, just kisses their dad on the cheek.
Derek tells his dad about Genim at dinner. Everyone stares at him like they know something.
--
Derek keeps his promise to Claudia, even when he's twelve and little kids are dumb. Genim is never dumb. He's very smart and he talks a lot, even though he's only five. Derek walks Genim to kindergarten every day because the middle school is right next to the elementary school. He makes sure Genim gets inside okay and gets his coat hung up. Derek always makes sure to glare at Jackson Whittemore because Genim always says he's mean.
When the school day ends he goes and waits outside the school for Genim to come out and then Derek holds his hand and walks him home.
--
Derek's mother tells him at fourteen what Genim's honey-home smell means. He doesn't smell like baby anymore, it's been replaced with grass.
"It means he's your mate," His mother tells him while she's cooking.
"Like you and dad?" Derek asks, watching his father watch his mother. They always look at each like they're more important than anything else.
"Yes," His mother says, and smiles at him, "Exactly."
--
Derek keeps his promise even when he's sixteen and wants Genim to grow up enough for him to know about mates.
Genim hates his name. Derek still likes it, but that doesn't matter, because the kids in Genim's grade make fun of him, everyone except Scott. Derek likes Scott, mostly because he watches out for Genim when Derek's in school, too, doing Algebra or reading Shakespeare.
"What should I call myself?" Genim asks, bumps his shoulder against Derek's to get his attention. "Something cool."
Derek shrugs, "I don't know."
Genim hits his arm, "Dude! Help me. Jackson Whittemore's a big jerk and keeps calling me genital."
"That doesn't even sound the same." Derek tells him, pats Genim's shoulder.
Genim pouts anyways, "Yes, it does."
"What about Stiles?" Derek suggests, tugs Genim in against his side, underneath his arm.
Genim perks up, "Like my last name!"
"Exactly." Derek tells him and Genim beams.
"Stiles."
--
Genim has been Stiles for two years when Derek is filling out university applications. Stiles is lying on his bed, helping him, because Stiles is smarter than him. Derek doesn't really feel bad about it, like Laura does, because Stiles is smarter than everyone and Derek is just proud of him.
"Dude, why are looking at community colleges?" Stiles rifles through Derek's papers.
"I don't want to go too far," Derek says over an application to Beacon College. He can't exactly leave his mate when Stiles is about to go through puberty. Derek needs to help him. Besides, Claudia is sick, and Stiles is too stubborn to call Derek for someone to talk to.
"But, Derek!" Stiles protests, flails into a sitting position, "You're, like, a genius. You could go anywhere. Berkeley has already offered you a spot!"
"I don't want to go too far." Derek insists, scribbles John Stilinski down as his non-familial emergency contact.
"You need to get out of this town," Stiles says, "You're way too good for it."
"It's my home, Stiles." Derek tells him, sets down the application. Derek shrugs, "Besides, what would you do without me?"
--
Derek is nineteen and doesn't know how to deal with the wracking, gut wrenching sobs that Stiles is creating. His shoulders are shaking and the beeping of that flat line echoes in Derek's ears even as he sees a healthy Claudia Stilinski asking him if he'd watch out for her son.
Derek slides down onto the floor beside Stiles, pulls him in against his side and presses his nose against Stiles' buzz cut. He breathes him in softly, even as his honey-home-grass smell turns sour with grief.
At some point, John walks out of the room and sees them. Stiles has both hands fisted in Derek's shirt and is still sobbing, openly and messy against Derek's chest.
John sits down on one of the chairs across the hall and watches them, stares at Stiles until his son stops crying and falls asleep under the heavy weight of Derek's arm.
--
Stiles is seventeen and fucking delicious. And distracting. Derek is trying to get his Master's but all he can think about is the last time Stiles was in his bed, stretched out and talking about nothing in particular. They told Stiles about werewolves when he was fifteen and about mates the year after. He didn't seem to mind, seemed oddly delighted by the idea of keeping Derek around for the rest of his life.
Since, though, Stiles has been a torment on Derek's ability to focus. Stiles has grown into long limbs and big hands and a pretty mouth. He's developed a compelling voice and sharp eyes that drive straight through to Derek's center. Stiles is nothing if not a smartass, and now he knows that he's Derek's mate, which is the source for all of Derek's torture.
Stiles has a habit of sending Derek pictures, explicit pictures, when Derek's studying, as if he just knows.
Like now, Derek checked his phone ten minutes ago to a picture of Stiles' legs, spread wide as he sat on the edge of what looked to be his bed. If that had been it, Derek could deal. Except, it wasn't. The picture also contains Stiles wearing dark boxer briefs, the outline of his hard cock visible through the material.
Derek's phone has been buzzing since. He refuses to look at it.
Bzz.
Bzz.
Bzz.
Bzz.
Derek grabs it. He swipes a thumb against the screen and opens the feed of messages.
Stiles with the head of his cock, red and leaking, peeking from the waistband of his briefs. The next one is Stiles' underwear stretched down underneath his balls, making his cock arch upwards and his balls pull up high and tight.
Stiles with a hand around his cock, thumb pressing against the head.
Stiles with long fingers stretching down behind his balls, to the tight hole Derek can't see on the screen.
Stiles with come against his hand, dripping down his shaft and against his stomach.
Then text: Derek, I'm bored.
Then: Derek, I'm more exciting than homework.
Derek, I really want to suck your cock.
Derek's surprised he doesn't crack his phone.
Derek, at least come over.
He sighs, responds: Be there in ten.
--
Stiles is only wearing one of Derek's Henley's when Derek gets there. He's stretched up against the headboard and smells like fresh come, looks warm and sated. Stiles' eyes go dark when Derek peels off his jacket, though, and the spike of arousal in his scent is addicting.
"I told you," Derek says, falls across the foot of Stiles' bed, "We're not doing anything until you're eighteen."
Stiles' bottom lip pushes forward. Derek swallows hard. Stiles smirks.
"C'mon, I'm eighteen in two months." Stiles reminds him, lets his legs fall open. He's hard again and Derek has to restrain himself from pushing in between Stiles' thighs and sucking him off, show him what he's asking for.
"Stiles." Is what he says instead.
"Derek." Stiles responds, lets his head tip back to expose his throat.
Stiles is a virgin, untouched and wanting, reeking of Derek. It's something Derek doesn't know how he resists. His mate, inexperienced but desperate for the hard pounding of Derek's cock. Stiles would be flushed, he'd babble and swear, grapple with shaking hands against Derek's shoulders. Stiles would be loud, Derek knows. Would shout and groan and whimper, would make the most beautiful noises as Derek took him apart.
"Eighteen." Derek grunts, voice low and rough.
"Fine." Stiles snaps and moves one hand down his stomach, "I'll do it myself."
Derek is sure that all of the air in the room evaporates. Stiles hooks a thumb in his briefs and yanks them down to expose his cock. Stiles wraps his fingers around it, side of his fist nestled against the thatch of hair just above.
Derek watches, transfixed and brutally hard, as Stiles drags his hand up and down the length of his shaft. Stiles fucking gasps when his thumb slides over the head, back arching. His eyes are shut but his mouth hangs wide open. Derek wants to put it to good use. But, then Stiles groans on a tight downward stroke and Derek thinks he can wait.
Stiles is mesmerizing as he jerks off, arching his back and whining. When he gets close he gets frantic, hips stuttering and legs quivering.
"Derek." Stiles gasps and Derek's spine liquefies. "Fuck, Derek." Stiles' mouth is still hanging open.
Derek lunges up, stretching out above Stiles and pressing their mouths together. Derek pushes his tongue inside and reaches down, bats Stiles' hand away from his leaking cock.
Stiles whines against Derek's mouth as soon as Derek's hand gets a grip on him. It doesn't even take a stroke to make Stiles come, it's as if the feeling of Derek's hand on him is the tipping point.
Stiles spurts over Derek's fingers, pulls his mouth away to gasp brokenly, "Derek."
Derek groans, hips shaking with the effort of not dry humping Stiles like an animal. Instead he raises his hand and licks Stiles' come from his fingers.
"Fuck." Stiles sighs, then pushes at Derek's shoulders until Derek rolls off and bounces onto the mattress beside him.
Stiles pushes upright and swings around, fingers going for the button on Derek's jeans, "I am so going to suck you off."
"Jesus, Stiles." Derek gasps, grabs Stiles' wrists in one hand, "No. We are not doing that. Your dad will kill me."
"My dad loves you," Stiles argues, rolling his eyes.
"He won't love me if I let his underage son suck my dick," Derek insists, placing Stiles' hands on the comforter. Derek grabs the front of Stiles' shirt, well Derek's shirt, and pulls Stiles in for a kiss.
"Two months." Derek says firmly, kisses Stiles again.
"But your birthday is next week," Stiles points out, "How are we supposed to celebrate?"
Derek thinks immediately of Stiles sticky with icing, writhing as Derek sucks it all off. "We have a stupid party that my parents host and you give me a comic book, same as every year."
"You're passing up on birthday sex?" Stiles grumbles, mouths along Derek's jaw before biting sharply.
"Yes." Derek says, voice shaky.
"You suck." Stiles snaps, flops away and onto the bed.
"Eventually." Derek says, smirking.
Stiles hits him with a pillow.