I remember watching a anime in early 2000 (the series itself may even be older) It was about a young girl and boy who were getting chased by a group of thiefs.
The girl possesed some sort of blue jewel/gem which they were trying to steal. And in the end the boy and girl prevented some kind of world war/domination plan. Also the girl found out some information about lost family during the journey I believe
The girl had black hair, and allot of jewelry. I also believe she had a red vest with a white shirt underneath it. The clothing looked a bit like that of a pirate.