Okay so I've actually spent way too much time thinking about this ship, which is funny because on the surface they barely interact in 'Demon Slayer'. That's kind of the point, though? A lot of fics start from that blank space—two incredibly traumatized, quiet guys who've been through hell and express it in opposite ways. Obanai's bitterness and possessiveness versus Muichiro's literal amnesia and emotional detachment.
Most writers I've seen latch onto the potential for a really fractured, slow recognition. Obanai, who holds onto his pain like a weapon, meeting someone who just... forgot theirs. It creates this push-pull where Obanai might initially dismiss Muichiro as an airhead, only to realize the depth of his loss is somehow even more profound. The fics that work best don't rush the romance; they let Obanai's harsh exterior slowly chip away as he sees a reflection of his own broken child self in Muichiro, but without the memory to contextualize it.
There's also a surprising amount of fanart and fics that play with their shared connection to snakes and mist, weaving those elements into the symbolism of their relationship—something elusive and potentially poisonous, but also protective. I read one where Obanai's snake, Kaburamaru, becomes a bridge, sensing Muichiro's calm and guiding Obanai toward it. The dynamics are less about grand declarations and more about two people learning to communicate in a language without words, built on shared silences and the weight of a past they can't fully articulate.
It’s niche, but the writers who get it are doing some of the most quietly intense character studies in the fandom, honestly.