The B Rank Missions are only assigned to to experienced ninja. With these missions you are able to unlock villians and subordinates of the most dangerous ninjas.
Win 1 battle with Gaara of the Desert versus Rock Lee. (1/1) Win 1 battle with Gaara of the Desert versus Dosu Kinuta. (1/1) Win 1 battle with Uchiha Sasuke versus Gaara of the Desert. (1/1) Win 1 battle with Kaguya Kimimaro versus Rock Lee. (1/1) Win 2 battles with Gaara of the Desert versus Kaguya Kimimaro. (2/2) Win 6 battles in a row with Gaara of the Desert. (6/6)