Honestly? I think the most compelling emotional conflict in Legosi x Haru fanfics isn't even about the interspecies taboo itself. That's just the set dressing. The real meat is in how writers translate Legosi's painfully earnest, overthinking nature into actual relationship hurdles that feel plausible within that world. You'll see stories where he's terrified his own strength might hurt her during a casual hug, not in some dramatic moment, but just because he got too relaxed and forgot to hold back. That constant, low-grade anxiety becomes a wall between them even when they're physically close. It's less 'society forbids this' and more 'my own body is a threat to the one I love,' which is way more intimate and heartbreaking.
A lot of writers also lean hard into the emotional maturity gap. Legosi is this big, awkward bundle of noble intentions and delayed development, while Haru has this sharp, weathered understanding of the world from living as prey. She's used to navigating danger and reading subtle cues for survival. So the conflict often comes from her being three steps ahead emotionally, anticipating problems he hasn't even recognized yet, while he's stuck trying to parse his own overwhelming feelings. She might withdraw as a self-preservation tactic, and he misreads it as rejection, spiraling into more overprotectiveness that just makes her feel smothered. That push-pull of him wanting to shield her from everything (including himself) and her fighting for her hard-won independence creates such a specific, rich tension. It's not just will-they-won't-they; it's can-they-even-figure-out-how-to-be-together-without-breaking-each-other's-spirit.
I've seen a few that flip the script, too, where Haru is the one struggling with the weight of his devotion. Like, she feels guilty for 'taming' this powerful creature, making him compromise his instincts, or worrying she's become a weakness his enemies can exploit. That adds another layer where the conflict is sourced from her own complex pride and survival guilt, not just from his side. The best fics use the predator/prey dynamic as a metaphor for all sorts of relatable relationship anxieties—feeling too much, not feeling enough, being afraid your love is somehow damaging to the other person. That's what keeps me coming back.