Is there an official name for a fetish focused on ethically compromised female assassins/sidekicks in movies? If not there really should be. I think I have that one.
Kill Bill is of course packed with this type of character, perhaps most notoriously GoGo Yubari. James Bond had Fatima Blush and Xenia Onatopp. Sin City has deadly little Miho, who might not have been evil, but was certainly amoral. Also in the not evil but also not exactly good we have Black Widow and Angelina Jolie as Mrs Smith. In the comic book realm, and more as evil side kicks rather than assassins, we have Harley Quinn, Poison Ivy and Dr Girlfriend (who I always found strangely sexy).
The latest character to add to this list is Gazelle from the violent but highly entertaining movie Kingsman. It’s not exactly Citizen Kane, but it is an fine pastiche of Bond movies and the original TV Avengers. I particularly enjoyed watching Gazelle (played by Sofia Boutella) kill people with her prosthetic steel legs. If I ever make it to Supervillain status, hiring someone like her will be right at the top of my list, just after buying a hollowed out volcano for my headquarters and picking out the color swatches for my minions uniforms.