Tobias and Tris from 'Divergent' have a fanfic scene that’s basically built around the enemies-to-lovers backbone, but with this very specific military-dystopian flavor. It’s not just about bickering until they kiss; the dynamic thrives on Tris being this stubborn, morally-driven newcomer and Tobias as the hardened, secret-soft mentor. A lot of stories dig into the power imbalance—he’s her instructor, she’s his student—and how that tension doesn’t just vanish when they get together. You see a ton of fics exploring the aftermath of that, like ‘what does this relationship look like when they’re finally equals, or trying to be?’
Another huge angle is the ‘hurt/comfort’ tag taken to extremes, because canon gives you so much material. Tris getting shot, Tobias dealing with his father’s abuse, both of them just constantly bruised and battered. Fics love to have one of them patching the other up, literally and emotionally. It gets tied into a protective streak, especially from Tobias, but then writers will often flip it and show Tris protecting him from his own demons, which I think is a stronger take.
I’ve also noticed a subset of AUs that shift them into modern settings, like college or coffee shops, but even then they keep that core dynamic of her fierce independence clashing with his guarded, world-weary attitude. The most popular ones somehow preserve that Dauntless intensity even without the factions.