The "four whores of the apocalypse" are the four main Diamond dogs and can-can dancers they are; Nini legs in the air, Mome Fromage, China Doll and Arbaia.
They appear to be a close group of friends and are normally seen together during most of the movie. Despite being close friends their appearances and personalities differ greatly.
Nini is the main can-can dancer of the Moulin Rouge and the star after Satine. This causes Nini to hold some bitterness towards Satine that may motivate her cruel actions in informing the duke of Satine and Christain's affair. Like the other Diamond dogs little is known about Nini's past, however by her overall attitude and behaviour it is reasonable to assume that she was pove.
This life style of poverty and prostitution on the streets of Pigalle, Montmartre and in the Moulin Rouge has left a deep effect on Nini. She is bitter and cynical especially towards romance. Despite this she forms a somewhat romantic relationship with the Argentinian. Whether it is a business relationship or romantic one is hard to say, although they are seen together throughout the movie.
However out of all the can-can girls, Nini is the best dressed which suggests that she is indeed competing with Satine. She has four costume changes. Her most memorable being her black tango dress and her can-can dress.
