You'll see a lot of Shinra dealing with his guilt over being part of a group that hurt Iris's family. A lot of fics explore him trying to atone for the sins of Avalanche, not just towards Tifa, but especially towards Marlene, and Iris gets drawn in as he tries to navigate that. It's a pretty solid foundation for angst, which fans seem to lean into heavily. They'll also bump up the age gap, making Iris slightly older or aging her up post-canon to avoid the squick factor, which is a smart move. There's also a weirdly high number of coffee shop or florist AUs for this pair, maybe because their canon interactions are so scarce that writers just transplant them into a gentler world to see what happens. The found family angle with Barret and Marlene pops up a lot too, with Shinra awkwardly trying to earn a place at the table.
Honestly, half the stories I stumble across are pure hurt/comfort. Shinra gets injured on a mission, Iris finds him and patches him up, leading to some forced proximity while he recovers. It's a classic for a reason, I guess. It's a niche ship, so the tropes tend to be pretty standard across the board—nothing too outlandish, mostly playing it safe with established dynamics from other fandoms.