Gunslinger Girl, Shikabane Hime: Aka Recommendations
Both are about girls that have guns and they both have a man with them that tells them what to do like a handler/monk. And their handler/monk can treat them however they like, a good friend, or just a piece of garbage. Although GS is more realistic.
Shikabane Hime, in my opinion, is basically a paranormal fantasy version of Gunslinger Girl. The monk/Shikabane Hime pairings are similar to the handler/cyborg Fratellos in Gunslinger Girl (though in GSG the handlers are exclusively male adults), both have a heavy focus on relationships between the members of these pairs, the inhuman characters in the pairs are always female, those same female characters become what they are due to extremely traumatic experiences, and both ask you if the girls can or should be considered human beings anymore.