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 Uzumaki Naruto versus Momochi Zabuza. (1/1) Win 1 battle with Uzumaki Naruto versus Haku. (1/1) Win 1 battle with Uzumaki Naruto versus Inuzuka Kiba. (1/1) Win 1 battle with Uzumaki Naruto versus Hyuuga Neji. (1/1) Win 1 battle with Uzumaki Naruto versus Gaara of the Desert. (1/1) Win 1 battle with Uzumaki Naruto versus Yakushi Kabuto. (1/1) Win 1 battle with Uzumaki Naruto versus Kaguya Kimimaro. (1/1) Win 2 battles with Uzumaki Naruto versus Uchiha Sasuke. (2/2) Win 6 battles in a row with Uzumaki Naruto. (6/6)