Finn x FP fics live and breathe by the whole 'enemies to lovers' energy, obviously. That initial dynamic where he's the reckless hero and she's the walking 'seriously, do not touch' hazard gives writers so much to play with. The classic 'whoops, I burned you during a friendly sparring match' followed by the frantic healing and awkward apologies never gets old.
But beyond that, I see a lot leaning into the 'stable force meets chaotic force' idea. Finn brings his boundless, sometimes naive enthusiasm into her more isolated, controlled world of royalty and fire powers. Writers love exploring how his straightforward nature cracks through her formal upbringing. There's also a surprising amount of 'hurt/comfort' centered on Finn's robotic arm—scenes where the metal gets superheated or malfunctions, and she has to carefully help without making it worse. It's a tangible way to show trust building.
I've noticed a sub-trend of fics that flip the script, though. Instead of Finn taming her wild side, they focus on Flame Princess learning to embrace her own intensity with him, not in spite of him. The romance isn't about calming the storm, but dancing in the rain of fire, you know? That feels more true to their characters to me than some of the softer, more generic takes.