Every time I reach a point of thinking, "you know, I really don't care much for Snape/Luna," along comes a fic like this one to show me how wrong I am. I like the starkness of the setting; it's elemental, for both of them, and that return to basics is ehat makes this relationship believable for me. I like your characterization of Luna: definitely different, but not loony.
Among the many fine lines: She was out of focus, but that didn't matter: in some ways, Luna was always out of focus
He had loved Lily, but he hadn't always liked her. Unknowingly, perhaps, she had always demanded something from him - expected him to be different. Luna expected nothing.