Soooo... Let's see... We have a masochist senpai, a sadistic kouhai, a BL manga author girl that just confessed, a stalker imouto, and a 5th one that has a smell fetish...
If it was me, i'd exclude right away the kouhai, as i don't have any interest in being a slave, and as the BL girl is too obsessed with it, it would creep the hell out of me, so 2 down. Even if the imouto would happen to be the "Cinderella", it would be freacking impossible to date her, incest and stuff, so another 1 down.
From the 2 girls left, the one that I would be less creeped out from her fetish, and I find more harmless, would be the senpai, even so that if you ""guide"" her correctly, she would end being a normal girl, but would have the eventual play.