Alright so I'm sleep-deprived enough that I can't be wordy about it for the most part, but here are my top-tier recommendations:
Mavet by JustAnotherGhostwri ter - This story is somewhat over 9,000 words long, and the only thing I can tell you is that the story starts in Megamorphs #3. To say
anything else would ruin a poignant, beautiful tale and clever character study.
All Flesh is Grass by Anonymous - Okay so this one is short (barely 2,000 words long), but it doesn't need to be long. WARNING IN ADVANCE: This fic features, as described by the author in the tags, "Vivisection, Dehumanization(...de-alienization?), Living anatomy model used repeatedly for painful/invasive medical procedure practice, Anesthetized patient nonconsensually used for invasive exam/procedure practice/training by students." This fic is
openly disturbing and pulls no punches, painting in the process a disturbingly realistic but narrow window into a Yeerk-run world.
Command, by Derin - Okay so this one story is the source of like half of my characterization of Visser Three as a character and I just have to own up to that. It's over 2,000 words but not more, so it's again pretty short and easy to read. It follows Esplin having a particularly average day, but from his perspective.
The Freedom That Unites Us by crosscrow - It's just over 12,000 words, and while it's creating a strangely fitting and unusual relationship between Eva and Alloran, it also features quite a bit of Alloran and Esplin's intensely toxic relationship in a way that I just...haven't been able to stop thinking about for years. Read it and cry, as I did. Read it and feel better, as some will.