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 Nara Shikamaru versus Tayuya or Temari. (5/5) Win 4 battles in a row with Nara Shikamaru. (4/4) Win 5 battles with Akimichi Chouji versus Dosu Kinuta or Jiroubou. (5/5) Win 4 battles in a row with Akimichi Chouji. (4/4) Win 5 battles with Yamanaka Ino versus Haruno Sakura or Kin Tsuchi. (5/5) Win 4 battles in a row with Yamanaka Ino. (4/4)