It’s actually one of the less common dynamics I’ve seen, which is part of why it sometimes works so well when writers do tackle it. The tension rarely comes from canon events—obviously—so it has to be built almost entirely from implication and internal struggle. A good fic will latch onto their fundamental differences: Rukia’s duty-bound, seasoned warrior pragmatism clashing with Orihime’s gentle, almost naïve, but stubbornly hopeful worldview. The real pull for me is when the story makes their mutual care for Ichigo not a point of jealousy, but a shared, complicated burden. They’re the two people who understand that specific weight best, but process it in completely opposite ways. That creates a quiet, aching kind of friction.
Writers often use proximity forced by circumstance—being the ones left behind in Karakura Town, or assigned to some joint mission—and then let their contrasting coping mechanisms rub against each other. Rukia might retreat into stern training regimens, while Orihime tries to heal everything with kindness, and each finds the other’s method both incomprehensible and strangely admirable. The emotional tension builds from that slow-burn realization of respect, mixed with a frustration that they can’t fully bridge the gap. It’s less about will-they-won’t-they romance and more about two profoundly different souls trying, and often failing, to truly see each other’s pain, which ends up being far more intimate. The best fics I’ve read leave you feeling that unresolved ache right along with them.