No Regrets
As far as Dean is concerned, Cas is perfect in every single way. Except one. Cas is an alpha, just like Dean, and thanks to their alpha biology, it's almost impossible for them to be together, even though they're truemates.
No matter how much they research or what they try, nothing seems to cover up the wrong scent that comes from two alphas being so close for so long. Until Dean finds out about a new medical procedure that'll make him genetically an omega.
But, as with many things that Dean does, he hadn't really thought this through very well. The transition from alpha to omega is... difficult to say the least. Not exactly painful, but every time he turns around there's some new bit of awkwardness he has to deal with. But he can finally be with Cas without the smell making him feel awful, so it'll be worth it, right?
~~~
This fic contains descriptions of Dean physically turning from an alpha into an omega. The process will actually be described and not just glossed over. Omegas have female sexual characteristics in this universe. If the thought of any of that squicks you, please don't bother reading this.
Her Eyes