18(Demon Slayer)

An Au where the Hashiras(-Muichiro) are in a poly marriage(including Tengen's wives) but for some reason almost everyone is oblivious to that.

Cue a 5+1 type of fic of times that people should have realized that they were all together(like Tomioka taking his spouses to meet Urokodaki, Rengoku talking non-stop about his spouses, Uzui instead of saying just 'his wives' saying 'three of his spouses during the Red Light District mission, Sanemi acting softer when with his spouses or talking/mentioning them, Shinobu being both kinder when treating her spouses but harsher when telling them off for getting hurt, etc) and then the one time were maybe a few slayers(kamaboko squad or not) talking about who the Hashiras may date now that Muzan is dead or something like that only for someone unexpected(Murata or Inosuke) confusedly looking at the group and then asking out loud/shouting if the Hashiras had divorced or broken up.