Snape the Sub
Sev is used to having a master, in a very nonsexual sense, but a master all the same.
Now that he doesn't, he realizes he might have a predisposition for being a bit...submissive in the right situation.
Now that he's a free man, he finds that he is a bit overwhelmed with just how free he is.
So many decisions to make about a future he didn't think he would have. The day to day is now rife with too many possibilities.
Until a certain well-meaning and incredibly bossy know-it-all is put in charge of repairing the castle.
She tells him what to do, and he has no desire to disobey. That confuses him. But also pleases him. It pleases him even more when Hermione is pleased with him in particular.
Severus of course over thinks this so much that he ends up having an anxiety attack in her presence. And of course, Hermione walks him through it in the gentlest way possible.
Cue the first time Sev really falls into 'subspace'.
And thus a dom/sub saga is born with the role reversal I need to put in writing