It's incredibly easy to forget that Cas is an alpha. Not that Dean buys into that stereotypical bullshit about subgenders anyway, it's just that… Well, Cas just doesn't do anything that normal alphas do.
Like, for example, Cas is an accountant. Technically, he does own his own firm, so he doesn't answer to anyone, but that's just so he can do bookkeeping for small businesses who sometimes can't pay with money. Cas will take basically anything. It's how he got the beehives in the backyard. It's how he got his big Heinz Fifty-Seven mutt, Claire ("That's a stupid name for a dog." "I can't rename her now, Dean, it will confuse her."). His computer, which Dean can only assume has nuclear launch codes and could power a small village, came from Dean's friend Charlie, who runs her own IT business next door to Cas'. When Cas discovered Dean's penchant for pie, he struck a deal with a baker, so Dean gets one freshly baked once a week.
Most alphas, though, if they even are in an office setting, are high-powered executives, who run multi-billion dollar companies, with thousands of employees. Cas' is a one-man shop, no one to boss around there.
Cas also does things like yoga, and meditation, and counting to ten. Alphas are warriors. They box and spar and fight. Cas is just… Real, real bendy. Which Dean is not complaining about, and he never will, and he never has, but it's… Different.
They've only been doing this for a couple of months, after Cas stuttered out a question, finally asking him out after a solid two weeks of Dean having to invent reasons to come visit Charlie so he could ogle the alpha. Whatever this is, it's going well, as far as Dean is concerned. A little weird, maybe, but nice.
Weird in that Cas doesn't… He just doesn't do the things that alphas do. He doesn't insist on paying for their dates, but is willing to. He doesn't check out Dean's ass (that the omega can see, anyway) every time he turns around, he doesn't get overly handsy, he doesn't push for sex at every opportunity. It's like he's just happy being around Dean.
That mentality blends into everywhere they go. When confronted with another alpha, most alphas will posture, or growl deep in their chest, or something. Not only does Cas not do any of that, Dean has even seen his alpha tilt his head and bare his neck in submission to avoid a confrontation. It's completely unheard of, at least to Dean, who grew up with John "I Would Die Before Baring My Neck to Another Alpha" Winchester.
And, listen, the sex. The sex is good, it's amazing, mind-altering, world-shattering good. It always leaves Dean jelly-legged and dazed.
So it is good, but it's gentle, tame. Cas picks him apart, yeah, disassembles Dean until there are tears running down his temples and he's straight-up begging, cock curved up to his belly, precome pooling, legs shaking, slick soaking the sheets beneath him. The only really alpha thing that Cas does is edge Dean until he's a mess, then makes him come so hard and fast that his vision blacks out and reality ceases for just a moment, nothing is real outside of the heat of Cas' mouth or the way Cas' big alpha cock fills him up.
But he never pushes Dean around, or manhandles him. Cas' kink is enthusiastic consent, and in a world where not everyone feels that way, Dean can get behind that, he really can.
It's just that Dean really, really loves being manhandled, and he hasn't found a good way to bring it up.
Other than that, Cas is a good alpha. He doesn't care that Dean is a firefighter who goes into burning buildings, he doesn't ask if Dean is "straining his delicate omega sensibilities," or whatever the fuck it is that's been shouted at him a million times since he started. At most, when Dean has had a bad day, or is dead tired, he'll put Dean on the couch after dinner, head in Cas' lap, and run his long, strong fingers through Dean's short hair until the omega falls asleep, wrapped in the scent of alpha and warm and safe.
He doesn't make snarky remarks that Dean can cook, or that Dean's house is clean, and they haven't discussed pups yet, but Dean knows that Cas wouldn't say a damn negative thing if Dean told him that he wants a huge houseful of them. He'll just hit Dean with those big blue eyes and quirk his lips in the half-smile he does so well.
So Dean is content, which is weird, but surely he'll get over it.