Villainous group of science fiction

SITH

["Dark-side wielders from a galaxy far, far away who follow the Rule of Two."]

The clue "Villainous group of science fiction" points to the Sith, the dark side-wielding antagonists from Star Wars. The word "group" hints at their collective nature as an order, while "villainous" directly describes their role in the franchise. "Science fiction" narrows it down to a well-known series, making the Sith the clear answer.