I've always found the fanfic take on 'Citrus' to fill in a lot of the gaps the manga left hanging, especially around personal growth. Yuzu's journey is the most interesting part, right? In canon she's this bundle of chaotic energy, but a lot of authors pick up on how that energy masks real insecurity. I've read a few fics where her relentless optimism is actually a coping mechanism, and her growth comes from learning to be vulnerable, not just cheerful.
Mei, on the other hand, gets a lot of backstory exploration that the source material only hints at. There's a fic I can't remember the name of that centered on her learning to want things for herself, not just out of duty. The growth isn't about her becoming 'soft'—it's about her developing a spine that's her own, not her family's. The best ones make their progress feel earned, not just because they're in love.
Honestly, sometimes the romance itself is just the vehicle; the real story is two people who were pretty stunted in different ways figuring out how to be actual, functional humans, together and separately.