I love your coldly assured narrator! The Book Thief is one of my favourite books, and I can see its influence here, but you've made the narrative device your own with the personality of your narrator.
This is a brilliant portrayal of how humans can hurt one another - the way the demon is nearly incidental to events, at least until near the end, despite its intentions. I am very much an Albus (and Aberforth!) fan, but found this interpretation of events sadly plausible.