Ichigo and Rukia arguing on who gets to be the protective one is basically the bedrock of their dynamic, so fics where they're already a unit but facing external drama really dig into that. Soul Society tries to separate them, or a new enemy threatens Karakura Town, and the whole plot is just them silently agreeing to watch each other's back without needing to say it. It’s less about grand romantic declarations and more about the sheer, stubborn refusal to let the other fight alone.
There's also a lot of post-canon stuff that explores the weight of their respective duties keeping them apart, which honestly feels more true to their characters than a straightforward happy ending sometimes. You'll find stories where Ichigo, now a fully-fledged Soul Reaper with his own assignments, and Rukia, as a seated officer and later captain, have to navigate long-distance through garganta or brief, stolen moments between missions. The tension isn't will-they-won't-they, but how-do-they-make-it-work, which is a more interesting challenge to read.