Archer of Red

One of the Servants of the “Red” camp. A huntress who wears beautiful green clothing. Her charm points consists of those things on her head that look like animal ears and that thing on her lower back that looks like a tail.
Her true name is Atalanta. She is a huntress who is famous for her swift feet in Ancient Greek legend. Just as told in the original myth, she has the tragic past of being born as the daughter of a king and yet being abandoned in the mountains by her father. After being raised by a female bear and later adopted by a hunter who treaded into the mountains, she has developed her skills conspicuously, perhaps due to her latent talent.
There are three tales that she is famous for. The first is how she was chosen as a member of the Argonauts led by Jason.
The second is the extermination of the Calydonian Boar. The third is the dispute over her marriage. None of these tales had a particularly happy ending for her, and her distrust of men became extremely strong due to the third one in particular as well.
Atalanta liked none of them since these warriors acted more violent than necessary when they hunted. However, there was one man named Peleus who she was fond of, for he was the only one who approached her with a humble attitude.
The reason she is obsessed over children is due to her own origins. The despair she felt as a baby was just that strong. She would happily throw away her own life to become a stepping stone to realizing a world where all children are saved.
The reason she cooperated with Shirou is also because she clung to the idea that his wish would lead to her own wish. Since it is uncertain whether the Holy Grail would be able to grant her wish, his words which spoke of a clear form of salvation might have seemed just like the gospel to her.
She has two Noble Phantasms, but one of them would normally be impossible to use in a regular Holy Grail War, so practically speaking, her only Noble Phantasm is “Phoebus Catastrophe: Complaint Message on the Arrow.”
Her animal ears and tail seem to be the symbols and after-effects of a curse told of in her legend… or so they should have been, but she actually seems to like them.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia