Anime Profile: Gunslinger Girl

In Italy, a private organization exists called "the Social Welfare Agency". In truth, the Agency is not as innocent as it's name says. It specializes in cover assassinations ordered by the government. However, the weapon of choice is possibly the most chilling... children... little girls, in fact!

Taken from families that were wiped out in criminal attacks, these girls are cybernetically enhanced and brainwashed into forgetting their pasts so that they become remorseless, cold-blooded killers. Jose, a handler of one of the girls, Henrietta, is worried, however. Jose is finding it hard to fulfill his duties to the Agency, as he is constantly concerned that Henrietta will continue to lose more of herself as she undertakes more missions.

It appears that the characters don't age after they have the surgery since Angelica looks as old in the present time as she did when she first joined the agency (which based on what Rico said had to have been at least two years ago, probably more).