What a stunningly brilliant story! The way you weave the tiniest canon details (Healer Pye and the Muggle remedies used on Arthur - the absense of Kettleburn from the Sorting Ceremony) is just great. And I love the true story of the Fountain. It is rather remarkable that every fact from that book that we can check with canon shows a Dumbledore lie or, at best, a half-truth. All the more interesting to get this back story.
The details of the magical world are so evocative, too. The iron aftertaste of the blood potion. Breeding Thestrals when you can't see them.
And, above all, your brilliant characterisation of Kettleburn - who is Canon Kettleburn, only better, for me), of Millicent Bulstrode, of Severus-the-Ghost. And their interaction - all maimed, all wounded, yet finding comfort with each other.