When I first heard of Gunslinger Girl, I was expecting a much different anime. The title in English uses two slang terms, so I assumed it would be a playful anime about 'girls' as in 'sexually appealing young women', being 'gunslingers' as in 'carefree gun-loving outlaws'. So I was expecting something basically like Bubblegum Crisis Tokyo 2040 set in the Wild West, or like Trigun but with a mostly female cast. That's not what this is at all, and I have to say, I think the title is a poor choice, arising from a poor understanding of the connotation those English words have.
This anime is a serious dramatic work set in Italy, where a government organization "helps" abandoned or traumatized little girls by making them into cyborgs and training them as assassins. It makes sense from a tactical standpoint, because as long as the organization is secret, most people don't suspect a little girl as a potential threat.
The girls are paired with handlers, men who are responsible for their training. Sometimes, the girls develop affection for them, sometimes, it's all business. Often, we see the handlers try to do nice things for the girls. This is usually out of pity, since the girls all have traumatic pasts and a difficult job. The anime is not really "slice of life" in the usual sense but it has that feel. Many episodes are just "a day in the life of _____", wherein a different girl is given the spotlight. But the anime focuses primarily on Henrietta, the girl with short brown hair.
Manga by Yu Aida
The Ending Song is Beautiful
While Gunslinger Girl isn't what I expected from the title, it was very good anyway. A lot of times, there are shows about cute girls fighting to save the world, and because it's all done with goofy recycled animation magic effects, the suffering and damage they dish out feels removed from reality. But in Gunslinger Girl, real-seeming little girls are forced to fight terrorists and the mafia, and because it's realistic, it has more emotional gravity to it.
Gunslinger Girl raises many important moral questions too. The girls are basically owned by the government, and their "welfare" is not for benevolent reasons, but for what the kids can do in return. Similarly, it has parallels in criticism of the welfare state, where it could be argued that the welfare is not for the good of humanity (as some claim) but rather as a political tool to buy public loyalty, approval ratings, and votes. In the same fashion, the girls are being helped, but only to be made into tools to be used by others.
I would recommend Gunslinger Girl. It's similar to Puella Magi Madoka Magica, but it doesn't have such an over-the-top melodramatic feel, it's just about the girls trying to make a good life for themselves, making the best out of their bad situation. It's sad, but it hits more hopeful notes sometimes, especially when you see how much all the girls in this situation work together and become sort of family to each other.