The dynamic between Kota and Eri is fascinating because it’s almost entirely fandom-crafted. Canon gives us a few crumbs—their brief, quiet moment after the festival arc—and the community ran with it. The most popular trope I see is the 'found family/older brother & little sister' dynamic. Writers love exploring Kota becoming her unofficial protector or guide at U.A., someone who understands what it’s like to be a kid impacted by villain violence in a deeply personal way.
Another huge one is 'healing together' fics. Stories where they navigate their respective traumas—his parents' death, her years of abuse—not through big conversations, but through small, shared moments. Like Kota teaching her how to throw a proper punch (for self-defense, obviously) or Eri sharing her apples with him. It’s less about romance, which feels off given their ages in most timelines, and more about building a quiet, solid friendship that helps them both move forward.
There's also a subset of future-fics where an older Kota, now a pro hero, occasionally checks in on a teenage Eri, offering advice she can’t get from Deku or Lemillion. It fills a niche for gen fluff that’s specific and heartfelt.