I am 24 now, I remember seeing this anime movie when I was very young(around 10 I think).
It was about a main character(who I believe was named Ariel). There was some kind of alien/monster that she was on a hunt to kill. Several scenes would show loads of dead corpses of its victims, massacred. At one point she comes across these 2 kids who are causing her trouble, I think they are throwing/shooting rocks at her. They appear to be boys and at some point one of them joins her. While in a apartment a dark skinned man shows up(which I think is Ariel's partner), he smells the air, and tells her that the little boy with her is actually a girl. At this point the little kid lets her hair down, and she looks more feminine(before i think she had it in a cap/hat). Near the end they are fighting the enemy and the little girl/kid has been putting together this staff look trap/device. The little girl uses it on her and Ariel to survive an attack from the enemy. It creates a forcefield/statis and protects them inside it. The little kid makes a quote "I was going to put you inside this thing."(referring to the enemy).
At the end they are riding off on some kind of vehicle. Seems like they are in the desert. They joke that without sun-glasses you can go blind.
Please help me find out what this is, it has been the curiosity of many failed google searches .