I've read a ton of fics for this pairing, and what gets me is how writers use the established roles from the show to flip them on their heads. Hawkodile starts off as this brute-force guy, all muscle and grunts, but in a good fic, you see him learning to be vulnerable. It's never just 'oh now he's soft.' It's him struggling to find words, trying to protect Fox not with his fists but by actually listening to her crazy plans. And Fox! She's the brains, but fanfiction loves to give her these moments where her logic fails, where she has to admit she needs backup, needs someone to pull her out of her own head. The growth feels earned because it plays with their core traits—strength becomes emotional openness, intellect becomes wisdom through collaboration. I read one where they were stuck in a puzzle room from one of Fox's old inventions, and he had to solve the physical parts while she untangled the code, and by the end they were basically finishing each other's sentences. It's that kind of synergy that good stories build toward, turning a fun action-comedy duo into partners who genuinely make each other better.
Some writers go darker, exploring Hawkodile's past regrets or Fox's fear of failure, which adds layers the show couldn't. It's not always smooth; sometimes the character growth is messy, two steps forward one step back, which makes it feel real. I've seen fics where they bicker for chapters because Hawkodile is overprotective and Fox feels smothered, but they work through it because they've built too much trust to just walk away. That conflict-driven growth hits harder than any fluff piece, even though I love those too. The best explorations make you believe these two could actually retire from the superhero life someday and run a weird, wonderful detective agency together, perfectly balanced.