Man, the amount of fic I've scrolled through for those two is kind of hilarious in hindsight. The 'reluctant allies to forced proximity to lovers' pipeline is basically a superhighway in that fandom. A lot of authors really latch onto the visual of Fuli being so fiercely independent and Kion being this born leader who has to respect that, but can't help wanting to protect the Circle. So you get a million variations on them getting separated from the Guard during a storm or a skirmish, having to rely on each other to survive, and all those prickly barriers just melting away. It's classic, it works.
Then there's the post-'Lion Guard' era stuff, which I find way more interesting. Fuli as the fastest, covering the most territory, and Kion as the king of the Tree of Life—that distance creates this whole vibe of longing and secret reunions. The angst potential is chefs kiss. I read this one where they'd arrange to meet at this specific watering hole halfway between their territories, and the entire story was just these quiet, charged moments of grooming and shared kills under the stars. No big drama, just the weight of duty versus this deep, private connection. It hit different.
Less common but my personal favorite are the 'what if' AUs where their roles are swapped or altered. Saw one where Fuli was the heir to the Tree of Life and Kion was her guard, all that loyalty and speed turned inward to protect her. The dynamic flip was super cool to see. Honestly, most of the popular plots circle back to that core tension: her need for open plains and his ties to pride and family. Whether they solve it with compromise, tragedy, or just running away together, that's the engine for most of the big stories.