Oddly enough, I have to begin my review with that line because it's the most graceful handling of Blaise's mother that I've ever read.
Grace is what this story exemplifies, I think, from the pacing, character development, and ease with which you expand upon the wizard world and present it as a mysterious one—something that I appreciate a great deal. A sense of wonder is what I felt when reading the first book in the series, and I've missed that feeling as much as your Harry has missed feeling happy. It seems entirely appropriate that Snape should be the one to save Harry from his unhappiness; he's always saving Harry, and he's able to save him here because his own altered state of being and action allow him time to reflect and grow. In no way can I object to how either man develops, no matter that Bai Wei bears little resemblance to his younger, more established self. Within your vision, everything unfolds with a lush, informed ease.
I'm grateful to have read One Down, Two Across precisely because it does bear little resemblance to the mainstays of the Snarry sub-genre; you've taken your subject and elevated it, reinvigorated it, and illustrated how to travel more deeply into the magical world. This is a transformative tale, and I come away from the reading of it having been transported in the most delightful manner. The only sadness for me is that I'm home again, my journey over, but it pleases me more than I can express to know that Harry and his family's journey is just beginning.
To classify your story as a Snarry one would be too limiting, as what you've written unifies the sub-genre of Snarry with literature. Your story is a gift to everyone who believes that Snape and Harry live, endlessly incarnated in innumerable plains of existence; in your words, you capture the beauty of one such dimension, with all its possibilities for hope. It was my sincere privilege to have experienced the magic of your story, and I thank you for the wonder that I felt in reading it.