The series follows the story of two young female assassins who embark together on a personal journey to seek answers about mysteries from their past. While at first they seem to be only vaguely related to each other, there are clues and hints given throughout the series that there are more than meets their eyes. During the course of the series, they are lured into more and more traps by a secret organization named Les Soldats ("The Soldiers" in French).
Noir was followed by two spiritual successors, Madlax and El Cazador de la Bruja. Together, these series constitute a trilogy exploring the "girls with guns" genre.
I believe it is a Bible of all the Girls with Guns Genre