i don't have that many and i haven't read much during the times when i was working on a long fic of my own, but here's my humble top-5 in no particular order:

Iterative - https://archiveofourown.org/works/4337213 - T | Gen, M/M.
the very fic that initially got me invested in the ship. after i finished it, i couldn't stop thinking of why the finale made me feel so hollowed, and me delving into the writing of my own was the result of this constant "why??"-thinking. in many ways, i felt like i couldn't contribute anything original or anywhere as good as this. and i vividly remember once getting a positive comment on RtD, where the author almost leveled it with Iterative: i ran hoppingly back home from work while mentally chanting "RtD got compared to Iterative! RtD got compared to Iterative!!". needless to say, it was the best praise ever.

Tidal Force - https://archiveofourown.org/works/196365 - M | M/M
Shadow Yu x Shadow Adachi. an interesting spin with very high quality prose (the author is getting published, so that level of mastery makes sense.. or so i would've said if a lot of published literature didn't suck nowadays, haha. anyway, this author's craft is superb!). i don't usually store metaphors from fics or any writing at all for a long in my memory, but the 'surprised dandelion puff' in regards to Adachi's hair is something that's forever stuck in my head for some reason.
(i also rarely like 2nd POV fics but it fits the Player character and is very well executed here.)

This Time I Won't Miss - https://archiveofourown.org/works/41430021 - M | M/M.
one of the scenarios i often contemplated about but never dared to explore in a fic because it's a very tough and excruciating process. so i was happy to see a similar idea brought to life and in such a well-done way, with a proper build-up and a great, in-depth character analysis. an emotionally intense, titillating, and devastating read.

One More, Partner? - https://archiveofourown.org/works/3876559 - E, M/M (with an easily skippable F/M bit if you're not a fan, like me).
one of those old-time, accomplice-ending, dubcon-adashu works where Yu still reads as a guy and not a 'babygirl'. the smut might be a bit too extreme to my tastes at times, since it's an E (while i prefer Ms), but the mesmerizing atmosphere of despair and an absolutely fucked-up abusive co-dependent relationship hits really hard.

The Court Jester - https://archiveofourown.org/works/41428860 - T | M/M.
a short but great spin on role reversal with a fresh taste of familiar (but, this time, sincerely) goofy Adachi and a very unfamiliar reserved and distant Yu. intriguing, heart-warming, and mentally stimulating in a way. i feel like this fic offers a lot of room for reader's interpretation of both Yu as a character and the adashu bond in this new context, so my gears started actively working, imagining this sort of dynamic with a darker Yu, upon the read.