biting as the common symptom of a young alpha developing one of their alpha instincts coming from the desire to put their mark on someone/something they consider theirs. and because they're still young, their canines are all also just growing out bit by bit, so there's this itching feeling to bite to relieve their gums.

teething little alpha sammy won't bite their alpha father and the only one he seems to want is his omega older brother dean who's yet to have his first heat either. but then john says it's fine, take care of your little brother. so dean does.

then he just has little sammy clinging to him at any possible moment he's able to, blunt teeth gnawing gently on dean's skin. dean's arms are filled with sammy's bite marks, small 'o' shapes of his little mouth. it's cute.

as sam grows and dean starts having heats, dean makes it clear that asking permission is needed and that sam can't immediately bite dean just any time he wants bc that's for little kids. and then sam would huff and puff and scoff before he pouts and looks at dean with wide eyes and a grimace, showing his blunt fangs, "dee, may i? please?"

only then will dean roll up his sleeves, grinning, "go on, little pup."

later, as sam's nearing the age where he'll start preparing to be a ripe alpha, his teeths are already changing to become sharper and ready for claiming. his bites that results in bleeding are more frequent and whenever he's looking for a place to gnaw, sam's starting to sniff higher and higher, from dean's hands to his shoulder until it's clear sam's eyeing his neck. dean starts wearing john's thick leather jacket and turn the collars up, he doesn't take it off when sam's biting, even when sam's glaring and scowling at the offensive jacket.

and then dean's heat hits, and this time it affects sam not in the cutesy, teething little alpha brother way that's cutely possessive. sam's holding him down, growling, pupils wide, mouth open showing his teeth. his canines are ready to take a mature, permanent, claiming bite.

it's probably good, then, that john chooses that time to barge in. he throws his jacket at dean's head, effectively covering him, and meets sam who's scrambling angrily at the interruption, immediately going to wrestle sam out of the room, though sam's fighting john off in order to stay. john drags sam out and dean doesn't see them again until his heat ends, and when he goes out, sam's already standing by the door, his tall stature slouching, his floppy bangs looking like dog ears.

dean barely notices the muzzle attached to his brother's lower face until sam drops to his knees and stares up at him, pouting behind the muzzle and putting on his puppy eyes as he says, "sorry, dee."

and dean, who's having a hard time reconciling the memory of being held down by his mature alpha brother with that same person on his knees in front of him right now, can only say, "uh, yeah. sure," and doesn't even have to reach far or bow down to ruffle sam's hair, sam's tall enough and he's already automatically tilting his head towards dean the moment he sees dean extending his hand.

"whatever, puppy," dean says, looking curiously at sam who's really enjoying the petting and the scratches as if he's an actual puppy. "what's with the new decor?"

sam scowls, "dad says i should stop biting."

"because you wanted to bite me? i was in heat and you're... newly mature. and you were too used to biting me all the time," he stops the petting to lean down, feeling over the muzzle to look for the latch and take it off sam's face. "he already got you out. isn't this a little too much?"

sam exercises his jaw once it's off, stretching his mouth, his canines are peeking out, but it doesn't feel as intimidating as it was. he stands up, looks at dean, sheepish, "i kinda bit his hand? and he got pissed."