We don’t meet Shijima until many chapters into Nabari No Ou, but once you ascertain certain key things about her, you realize she has in fact been lurking about the story in a different form since early on. I won’t spoil it for you, but consider her weapon of choice: claws.
What else?
-she surprises people with how much she knows about them
-calmly observes people and draws conclusions about them, so she’s easy for an artist-observer type like me to relate to
-ruthless in a fight scene, and one of the few to hold her own and even dominate against some of the most dangerous ninja guys in the story
-earns the trust of a leader-type in the story and is given a certain thing that everyone else would die to get their hands on
Never underestimate someone just because they look like a wee little girl. Shijima rocks!