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 10 battles with any Konoha Jounin (Pre-Shippuden). (10/10) Win 5 battles in a row with Baki. (5/5) Win 10 battles with Baki versus any Konoha Jounin (Pre-Shippuden). (10/10)