How about a detective story where a serial killer first seduces and takes young beauties in every hole. Then when he's done he says he has an idea. He ties them up and puts a special "cup" over their mouth and nose and stands and pees in it...making it look like he's drowning his poor victims with his pee. (Obviously you'd need girls like Gen who don't mind this kind of thing.)

The female detective and her lesbian partner (gotta have some girl/girl in this) track down the serial killer because he's targetting former lovers of theirs who are hiding their bisexuality.

I think it could be an interesting film.