I'll be real, I was so ready to get mad at the idea that anyone would even try to write this ship. Robin and Franky? From the 'One Piece' manga? It seemed like a total crack pairing at first glance. But someone in my Discord server linked this one called 'Blueprint for a Quiet Heart' on Ao3 and it completely changed my mind.
The premise is that Franky, post-time skip, keeps noticing Robin is quiet even for her. He starts making little inventions for her—a heated mug for her tea, a silent book light. It's told from his POV, and the author nails his over-the-top inner monologue slowly giving way to genuine worry. The burn is glacially slow because Robin is, well, Robin. She doesn't trust easily, and the fic spends ages on her just observing his actions, trying to figure out his angle. There's no big confession for like 30 chapters, just these tiny, cumulative moments of care that finally break through her reserve. It ruined me. I'm a sucker for characters who show love through acts of service, and Franky building stuff for her is the perfect vehicle for that.
Another solid one is 'Docking at Dawn,' which uses their shared history with Water 7 and the Poneglyphs as a backdrop. The slow burn here comes from mutual professional respect evolving into something more during long research nights on the Sunny. It's less about grand gestures and more about two very intelligent, guarded people finding an unexpected equal.