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"Where's your costume?" Stiles asks.
"I'm a werewolf," Derek says, deadpan.
Stiles shakes his head and laughs. "Of course you are," he says and kisses him. "Come on."
They get drinks and Stiles reintroduces Derek to a few of his fraternity brothers whom Derek has met several times, but who never remember him due to their extreme intoxication at the time.
It took a long time to get why Stiles wanted to join a fraternity—he has the pack, after all, what greater fraternity is there—but the pack isn't around when he's at school, and he's always been kind of a loner so it makes sense that he'd want somewhere he could easily belong.
The party is full of werewolves, witches, vampires, leprechauns, and fairies, some of which are actually human. Of course, there are plenty of cop-out costumes—slutty whatevers and jocks in their actual athletic uniforms—but for the most part people have gone all out. Stiles made it clear he wasn't letting anyone attend who wasn't in costume, and his fraternity brothers take Stiles seriously.
Stiles himself flits about the party as a raven, keeping up on his hosting duties. His costume isn't much—black jeans and a black shirt—but he has great feathered wings strapped to his back that somehow move as if a part of him. The painted-on black eye mask is speckled with silver glitter that lends him an almost ethereal quality. Derek can't take his eyes off him.
---
It's bizarre to watch Stiles' fraternity brothers interact unknowingly with these creatures of the night. Intent on having the most authentic Halloween party possible, Stiles invited all manner of creature the pack had befriended over the last few years. Everyone loves a party, he'd said. Even monsters like you.
"I don't recognize those guys," Derek overhears. He follows the speakers' line of vision and has to tamp down a laugh. Boyd is talking with Oona and Nixie, a couple of Merfolk they'd had run-ins with several years back but whom they've come to respect and rely on.
"Stiles said they're from D-Chi," someone answers.
"They're really dedicated to those costumes."
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Eventually Stiles gets Derek out on the dance floor.
"You've been watching me," Stiles says, as they sway together.
"Can't help it. That costume..." Derek looks him up and down, enchanted by Stiles' wings, which he discovers aren't strapped on at all. He can't stop running his fingers along Stiles' back where skin ends and wing begins.
"Leaf helped. They'll disappear after a few hours, but I thought it'd be fun to have real wings for a night."
"I like them," Derek admits. Stiles kisses him, long and slow. The DJ's exhausted his Halloween music stash and moves on to mood music as the party winds down.
"Come with me." Stiles takes his hand and leads him to the edge of the graveyard behind a huge crypt.
Stiles drops to his knees as soon as they're out of sight, wings spreading out behind him. He mouths at Derek's dick through his jeans—always so eager—while his fingers fumble with Derek's belt.
His dick is in Stiles' mouth before Derek can register cool, night air on sensitive skin. Stiles sucks him down hard and fast, no nuance or finesse in the act, just pure want. Derek fists a hand in Stiles' hair, guiding him back and forth with increasing speed. Tearing fabric echoes in his ears before he realizes he's torn Stiles' shirt clean off.
Shiny, black feathers practically glow in the moonlight. Derek runs gentle fingers along the edge of Stiles' wing and Stiles moans around Derek in response, feathers ruffling.
Derek feels his orgasm building deep in his gut. He has to move to lean back against the cold, marble wall because his knees threaten to give out. Stiles' fingers and mouth are insanely talented and he knows precisely how to take Derek apart. Then Stiles looks up at him through that painted on mask.
It starts as a low growl in the back of his throat. The shift overtakes him, quickly and uncontrollably, the moment he's finished coming. The combination of Stiles and the full moon is too much for his shattered control. He lands on the ground on all fours and howls.
The record screeches to a halt. When Derek looks up, he discovers he's fallen out of the protective shadows of the crypt and is in now full view of the party guests.
"Wolf!" Someone shouts. "Run!"