How do i become a ninja?

[Enkidoh]

Have you been doing the main story quests? Before you can switch to a Job/unlock Jobs you need to have played through the main scenario quests up to the level 20ish quest 'Sylph Management' which needs to be completed. Completing this quest will allow you to unlock Jobs for the classes. Main scenario quests are identified by a different quest icon (a flaming meteor icon rather than the usual exclamation mark in a speech bubble icon).