I found it back! That one web-story I spoke about before, where "Hansel and Gretel" was fused with "Little-Brother, Little-Sister"? It is part of the story written by lotdanccatte "The Roebuck-Prince, the Tower-Maiden and Iron Henry". It is part of a bigger (if not massive) multi-crossover of all the Grimms fairytales mixed into one epic narrative - in fact it is the first part of it, followed by "The Long Sleep" and "Iron Henry's Extraneous Tales".
All three of them form the series known as "Iron Henry and the Devil in Conflict" (aka Das Märchen der Märchen). It was @grimoireoffolkloreandfairytales who made me aware of the existence of this series, and you can see all the scholarly passion for fairytales poured in there through the "notes" section.
In fact, after this one epic of German fairytales, the author went on and did another "massive fairytale crossover" for... French fairytales, specifically those of Charles Perrault and madame d'Aulnoy, titled "The Courts of Glass and Briar", trying its best to imitate the style in which the stories were published in English... And this dedication to pastiching fairytale styles while studying their cultural areas led to a THIRD series: Cinche Cunti, overo Lo juorno de li juorne (Five Tales, or the Day of Days), this time based onto the Pentamerone.
And while it wasn't there last time I checked, it seems now there's a fourth "cultural entry" with Fairytales of the Gilded City - a fantasy version of the Gilded Age of New-York, told under the angle of Dutch fairytales?
