Looking at the code from 7A, you get it byI think using "Give up" at the start of a fight, then just using "pleasure stance" and only using "healing thoughts" when necessary raises charm.
I just unlocked floor 3, had a gangbang in the first two rooms by doing the skills I said and only those, without doing any sexual skills at all and my charm went from 27 to 33. Playing on Warden Mode btw, dunno if that has anything to do with it.
Edit: The guard in the guard room says that just standing there doing nothing and looking pretty raises charm, technically giving up and letting everyone have their way is doing nothing.
Edit 2: Ok so I got Flaunt while having 33 Charm and only one acc bought and equipped.
- greeting visitors
- giving handshakes
- flashing people and making them horny (in waitress battle too)
- serving drinks on time
- masturbating in battle
- getting cummed in or on (anywhere else won't help)
Btw charm decreases with the number of passives you have.