Ohhh, this is just so incredibly erotic even without any nudity involved (yet). The lighting filtering in through the window and slightly illuminating a dim room gives this a quiet, intimate, intense aura. The poses create so many suggestions.
Minerva is wonderful; I can really feel her character and her presence even though we can't see her face/head. The stiff, commanding posture, the buttoned up clothing, the prim yet form-fitting mode of dress. The cane/rod with the Gryffindor red gem -- nice touch.
And Snaaaaaape! Oh, how perfect is young, raw, new professor Snape here?? His pose and expression make it clear that he's entirely submitting to Minerva''s will. He looks ashamed; there are so many ideas and implications as to why he might need this at this particular point in his life. Also? Barely exposed neck and collarbones = OMG HOT FLAIL!!!