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 5 battles with Rock Lee versus Gaara of the Desert or Kaguya Kimimaro. (5/5) Win 4 battles in a row with Rock Lee. (4/4) Win 5 battles with Tenten versus Hyuuga Neji or Temari. (5/5) Win 4 battles in a row with Tenten. (4/4) Win 5 battles with Hyuuga Neji versus Hyuuga Hinata or Uzumaki Naruto. (5/5) Win 4 battles in a row with Hyuuga Neji. (4/4)