Let's see the options.
Henrietta: Saito would be king and bang every girl he wants ALONGSIDE Rietta.
Kirche: Sex all night
Siesta: As someone said before, Saito would turn her into a standard jap girl, aka, a slut.
Jessica: Would bang Saito given the chance.
Tiffania: After ep03 of PnR, Sex Ed daily for her.
Tabitha: Difficult one. Depends if she's able to tell Saito her past and real self.
Montmorency: valid rape to make her a better person :p
Agnès: same as Mon-Mon