Oh, Not-So-Myterious-Artist, this is definitely different for you (and not only because of the pairing), and really, really cool. Absolutely gorgeous. You've hit the fairy tale essence dead-on; it's very dream-like.
Snape's scraggly yet attractive. I love his expression of almost childlike wonder as he looks at Luna. And Luna is beautiful, sort of half sprite, half temptress. It's hard to say whether he's drawing her out or if she's drawing him in.
There are so many wonderful details: droplets hitting the water, the cattails, the moon and its reflection in the water, Luna's flowers, the texture of the tree bark. The grass and reeds and tree making a "frame" for the scene is a really neat effect. Fantastic inking on this, and great balance of light and dark.