1(Demon Slayer)

An AU where Zenitsu and Tomioka knew each other much before they met in canon with the reason behind it was Zenitsu being engaged to the younger brother of Tomioka's husband.

This is mostly me wanting to see the Hashiras and others reactions to finding out Tomioka is married and Zenitsu engaged(he flirts and asks girls to marry him because he likes to annoy his fiancé but they are both happy with the engagement) especially with the possibility of who said husband and fiancé could be(maybe an oc or a character from another anime?).

Also Tomioka and Zenitsu would be almost like siblings(also, maybe Sabito and few others could still be alive for this).

Anyways, anything else is up to the writer.