So the game is divided into episodes. Each episode focuses on a culprit and a specific fetish. The nurse tells you what you need to do (and do it in order) because going off track will result in unnecessary corruption.
Beat the boss at the end to move onto the next episode and fetish. Failure results in the game going down a different route with that fetish (revealing more plot points early on as a result). I'm kind of mad as hell though with how the bad ending 1 reveals all the important girls (and actually eliminating suspects as a result).
But yeah. Don't get sidetracked to avoid corruption. Probably is a different ending (or pertains to the masturbation scenes).