I actually need to push back on the whole idea of there being 'suitable' genres for these two; sometimes I think fans get too focused on fitting dynamics into neat boxes. With Sanemi and Tanjiro, the entire appeal lies in the massive, jagged edges between them. So a fluffy coffee shop AU would fundamentally miss what makes them compelling. You need a framework that forces that friction into collaboration or, even better, mutual survival. Post-Mugen Train or post-final battle AUs are obvious, but the real potential is in something like a body-swap scenario. Imagine Sanemi waking up in Tanjiro's body, having to navigate that relentless kindness and empathy from the inside, while Tanjiro experiences the constant, visceral anger of a Wind Hashira. The genre isn't romance or action—it's psychological horror with a side of forced character development.
I've seen some attempts at rivals-to-lovers that fall flat because they smooth over Sanemi's rage too quickly. The best fic I read recently was a canon-divergence where Tanjiro, post-recovery, is assigned to shadow Sanemi specifically for his endurance. It was a mission-focused, gen-heavy story with slow-burn undertones. The genre was basically 'mission fic,' but the tension came from close quarters and Sanemi's growing, unwilling respect for Tanjiro's resilience. A pure hurt/comfort could work if the 'hurt' is severe enough to bypass Sanemi's defenses—something that forces him into a caregiver role he's utterly unequipped for, making the 'comfort' awkward and fraught. Crossovers with similarly harsh settings, like 'Jujutsu Kaisen', could also work, trapping them in a domain expansion together. The genre should serve to amplify their core conflict, not soften it.