Noir takes its focus around two young assassins who work together in order to better understand their mysterious pasts. Mireille Bouquet, an established assassin, discovers a young girl on one of her missions who knows herself only as Yumira Kirika. This is simply the name that was given to her as a cover as a high school student. At first sight of Kirika you would think that because of her young age, and what appears to be inexperience she would be helpless, and of little to the hard hittin ass kickin Mireille. Once the fighting begins Kirika turns out to be anything but cannon fodder. She is able to match the talents of Mireille and may in fact surpass her in skill.

At first the relationship between the two is simply a matter of convenience and a mutual understanding that the other could best be used to understand their pasts. As the series progresses their relationship develops into a deeper one in which each of them is put in situations where they must rely upon the others skills. It is when these two begin working together that the plot of the story really begins develop. The two become known to the underworld as the angels of death for their speed and accuracy in the disposal of anonymous henchmen.