If it's in story mode I got the suit by going to the fortress on the left of the town.
Among the options, if you spy on the owner with his "girl" and then you make yourself known, he will make you his for several days.
After those days you will leave the fortress with a maid outfit, blonde and with a cage
Correct me if I'm wrong, but you said that nothing happens when you have the Prostitute class, but according to all my attempts to get Lady of the Night to level 20 and get that class Hiro becomes such a whore that he no longer charges for his services, In fact, he gives his ass for free if he doesn't pay himself to be fucked.
(I don't speak English, use the translate)
