Prince of Sieves

The story is about a jack of all trades, a tad insane (perhaps), who says he's a prince, leisurely wandering the land. The seat of his vehicle is a throne. His horse is re-dyed frequently.

Enter a girl who claims she's his sister, tough, independent who seems to draw trouble which she revels in.

It feels like a fantasy story but try a modern setting. (You may lose the horse if you wish.) Or future. The two could be aliens, maybe of different species. One or both could be androids.