I'm coming at this from a place of frustration, honestly. A lot of Revy/Rock stuff just... misses the point of their dynamic for me. They're not a cute couple waiting to happen; they're two broken lenses grinding against each other, and the friction is what makes it compelling. The best fics I've found lean into that ugly, raw tension without forcing a neat resolution.
There's an older one on AO3 called 'The Algebra of a Trigger Pull' that nails it. It's less about romance and more about the brutal calculus of survival in Roanapur, with Rock's moral compromises and Revy's violent pragmatism constantly clashing. The author gets that their 'closeness' is born from being the only two people in that hellhole who can almost understand each other's brand of damage, not from shared interests or sweet moments.
I've given up on anything labeled 'fluff' for this pairing. The good stuff lives in the 'angst', 'psychological', and 'unresolved tension' tags. A shorter piece I keep going back to is 'Double Tap,' which is just a single, intense conversation in the back of the Lagoon Company boat after a bad job. The dialogue crackles with that specific blend of contempt and dependency they have. It feels ripped right from the show's colder, quieter moments.