I am looking for an anime I saw some years back in which a young teenage heiress, who is being slowly murdered by her guardians, runs off with a world-famous thief. The story was probably set somewhere during the industrial revolution, because the thief had a dirigible that he and his crew used to travel. The girl is kind of adapted by the thief and his crew, and starts becoming one of them.
Also, as far as I can recall, there were no supernatural beings/powers in the story, though I am not very confident about it.