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 Inuzuka Kiba versus Sakon or Uzumaki Naruto. (5/5) Win 4 battles in a row with Inuzuka Kiba. (4/4) Win 5 battles with Hyuuga Hinata versus Haruno Sakura or Hyuuga Neji. (5/5) Win 4 battles in a row with Hyuuga Hinata. (4/4) Win 5 battles with Aburame Shino versus Kankuro or Zaku Abumi. (5/5) Win 4 battles in a row with Aburame Shino. (4/4)