Gunslinger Girl is an anime, a manga, and holy crap it's a video game now. o.O It's about a secret government agency that trains little girls as assassins. They find hospitalized girls with broken or nonexistent families, give them robotic parts, take them in to live at a special assassin facility, where they are turned into perfect, adorable killing machines, through rigorous weapons training, and conditioning. They use little girls because the conditioning takes better to younger subjects. Each girl is assigned a "handler", who personally sees to their training, and personally decides how much conditioning their respective girls are put through. If I had to point out main characters, they would probably be Jose and Henrietta. The girls and their handlers all get a fair amount of screen time, but those two seem to appear the most. Henrietta is the girl featured in the image above. Her weapons of choice are an FN-P90 smg w/ detachable suppressor, and a P239 Dual-toned 9mm pistol.
This series isn't some big killfest though. There's a lot of time spent on moral dilemmas surrounding the conditioning processes and the fact that these are little girls they're using to assassinate people. Jose differs from most of the other handlers, in that he regards his girl Henrietta as more of a person than a machine. He treats her just like a normal real girl, while the other handlers often have difficulty remembering that their girls are still human.
Gunslinger Girl is an excellent anime/manga series regardless of your personal tastes. You don't need to be into action or lolis to like this show. It's not sexual in any way, (well, I will admit the manga has a few panty shots) and the show's only violent when it needs to be. Gunslinger Girl is really about the story, and I love it. I could talk about this series all day long. I really hope they produce the sequel in America.