Vicki here, letting you know how good I think this story is. It does such an excellent job of filling in a lot of backstory about Gellert Grindelwald's actions in his later years, showing us why he was so feared and why Dumbledore eventually had no choice but to duel with him and take him out. I am reminded of stories about various assassination attempts, all unsuccessful, on the life of Adolf Hitler. Just by reading the seven books, I never felt that I had a good handle on Grindelwald, only a brief story of his adolescent predilections and some obscure references to his being a bad dude in later life, eventually neutralized by Dumbledore.
But you have certainly depicted a parallel between Grindelwald propagandizing against Muggles and Hitler propagandizing against Jews, both men being mesmerizing orators.
I loved your descriptions of locales -- the farmhouse in Leipzig, which used to have a shed outbuilding; stars, small rustlings, and night noises; the interior of the German Ministry of Magic. It takes only a few sentences, but I can see it all well in my mind's eye.
And I love that you have given us a big glimpse into Viktor's character by showing us the family he came from, their values and their actions. We see the principles that he has been taught; it is all very believable. He is more than just a burly Quidditch champion with a thick Eastern European accent. (Thank you for not trying to reproduce Viktor's accent when he speaks English. I see this story as an English translation of a story he tells in his native language.)
The pace of the story is excellent -- simple, unadorned story-telling. A story like this doesn't need adornment; in fact, adornment would detract. The facts speak for themselves.
I am glad you wrote this story. Viktor is an important minor character in the books, and we needed to understand him better. Your story has accomplished that.
My father was in the second world war. It was quite an adventure but he told some grim stories.