Oh, what a brilliant AU, and Aziraphale headcanon firmly accepted! Anathema as a Wren is perfect, and I agree with all those who have commented on how wonderful her and Newt's friendship is here. And Crowley's excuse for having yellow eyes, and the way he cares so much more than he'll admit about the humans he's working with, and the nod to the (awful) French translation of his name! And all the things Aziraphale can't quite bring himself to say in his letter! I love this; it's just perfect.