The girl is Airi, the Dog daimyou's little sister. She is kind of a whimsical person, and of course - since living in a samurai family - good with bow and wakizashi, the short sword.
She is fond of paper-folding and her favourite thing is to make them actually FLY with her special skill... She often uses it for spying, too. XD
She is just a side character, though has important role in the story.