*Sigh* This was simply lovely. I really like the way you write both Severus and Harry - I feel as if you capture what I love best about both of them just perfectly. Harry is so perfectly genuine, kind and honorable; and Snape is gruff and stiff, the restraint that Harry thinks he himself doesn't possess is Snape's constant companion. Yet his actions always belie the harshness of his words. The pacing of this was wonderful, making the building relationship very believable.
One of my favorite lines is: Later he apologizes by way of a curt nod and a passing mention of term-end preparations, which apology is accepted with a sniff and a questioning eye. I just love how this one little line conveys so much about both Severus' and Minerva's personalities.
Another: Of the varied sorts of fear that Severus has had occasion to contemplate, it seems to him that apprehension in connection with a social meeting must be the very worst. Of course the social would be the worst for Severus, with his emotionally closed off existence. The way that you had Harry so gently and warmly draw him out was just beautiful. Thanks for a wonderful story!