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 15 battles with Rock Lee versus any Konoha Ninja who is not part of Team 9. (15/15) Win 15 battles with Tenten versus any Konoha Ninja who is not part of Team 9. (15/15) Win 15 battles with Hyuuga Neji versus any Konoha Ninja who is not part of Team 9. (15/15)