This anime was shown in the earlier 2000's on Toonami.

I remember a boy with a sword who had to go on a journey around the world. He met a girl with brown hair, but he was reluctant to help in the beginning.

The girl had two guns that she called Uzis (I think), but they were shaped like this and were red and white:

I remember one episode where the girl had to get her guns fixed, or something, but the shop owner actually made them too powerful and they had a huge recoil when she shot.