Quote Originally Posted by MirageSniper View Post
Just to be clear, you would also need to complete the class quests for both the classes in order to unlock the job you desire. if its not letting you unlock it then its most likely that you didn't finish the class quest for the ones you need to level up to lvl15.
Class quests for the supporting class don't matter. The game only cares about Sylph Management and main class quests from 1 through 30. For ARC and ROG, the final class quests are The One that Got Away and Cloying Victory, respectively. Note that in the case of ROG, there are two Lv30 class quests; Cloying Victory is the second.