I see the characters strictly as symbols rather than constructs of fictional people we are meant to sort of relate to/empathize with if that makes sense.
Ibu and Ena are first love and sexual awakenings, the difference between them is Ena is willing to commit while Ibu is still reluctant.
Coach seems like the symbol of sexual freedom while Kaori represents the typical repressed woman who craves sex but does not dare speak it for the minute she does, she’s considered a dirty slut by society.
Yuni is the typical working adult, bored with her day to day life and looking for solace. In her case, it just happened to be the arms of an innocent middle schooler.
The thing that separates Yuni from Coach is that Yuni just seems to only have eyes for Ibu while coach wants all the girls if she can get away with it.