Oh man, the Doffy/Croc pair has such a weirdly specific niche energy that I'm surprised how much I've read. For me, the most compelling plotlines always lean into their shared status as former warlords and underworld kingpins, but with wildly different methods. The classic is the 'business merger' fic—some crisis forces them to temporarily ally their organizations, maybe a new World Government weapon threatens the underworld economy, and they have to navigate a tense partnership full of double-cross attempts and vicious boardroom negotiations that are just as deadly as any battle. Those fics thrive on their contrasting styles: Crocodile's cold, calculating patience versus Doflamingo's theatrical, chaotic aggression. Another plot I see a lot is the 'what if they met earlier' scenario, often set during the Void Century research period or Crocodile's early days in Alabasta. A less common but fascinating angle is post-Marineford, where a defeated Crocodile seeks out Doflamingo for revenge or an alliance, only to find their mutual bitterness creates a different kind of bond. I've always preferred when writers don't just go for instant romance, but let the tension simmer in their shared cynicism about the world—two men who wanted to burn it down for different reasons, now stuck figuring out what's left.
That business merger trope is fun because it lets you explore logistics—how Baroque Works and the Donquixote Pirates would even mesh is a nightmare. Who gets which territory? How do Mr. 1 and Vergo interact? The potential for internal power struggles within the alliance is endless. I'm less sold on the overly romantic 'enemies to lovers' stuff that glosses over how genuinely awful they both are; the best fics let them stay awful together, finding a twisted companionship in mutual ambition rather than redemption. A plot I'd love to see more of is one where they're forced into a semi-permanent arrangement by circumstance—maybe stranded together after a Marine raid—and the slow erosion of their guards isn't about love, but about recognizing a mirror in each other's ambition and spite.