This is just lovely! I'm hugging this story to my heart! Not a superfluous word or thought. You've masterfully and with such delicately rendered Rabastan's deficiencies and his gifts in such a way that he has the beautiful innocence of a child yet the profound wisdom of the artist. That Snape is the one to recognize his genius is so achingly poignant as well. Of course he would see in Rabastan what others do not, and have the integrity and courage to embrace it. And that Rabastan would see beauty in Snape... Divine.
I hope you've written many, many stories I can enjoy once your identity is revealed! I'm reccing this at once.