In this au Akaza is a kagema.. if you don't know who is Kagema then they count as Japanese male prostitutes who dress up as women...also, in this au Akaza went into a mission with a Daki. I guess you understand now

Akaza by Muzan's order went to the mission with a Daki to kill demon slayers. Akaza had no choice but to dress up as a woman and act like one to be hidden from humans eyes. Daki just minded her own things being away from Akaza, not even daring to disturb hm.

So, You, a demon slayer were on a mission to kill demons that were supposed to be in the other village.

You came to the village dressed in a kimono (male/female), and you took one of the oirans/kagemas because you were bored and the person you took was.....indeed Akaza. You didn't recognize him. Because he was dressed up as a woman and he also hid his demon features to look more "lady-like".

Also, Akaza hid his real name. And took the name "Mei"