The recommendation may have been from here originally but I can't find it now: To The Stars - incomplete, set in the far future of the Puella Magi Madoka☆Magica universe, contriving to shape the plot and tone into something resembling Starship Troopers (or more likely Old Man's War). I find the way it forces a fantasy story into quite hard sci-fi rather interesting; there are places where you can see the strain, but mostly it works well, and the characters strike a good balance, developed from but solidly rooted in their canon originals. I will say it's not that well written - the phrasing is distinctly clunky at times - but for me the plot, characters and especially the worldbuilding were good enough to shine through.