"Sages are those who have gained knowledge in all schools of arcane arts. They can use all types of spells!"
The Sage(賢者,Kenja?) is a Job class in Final Fantasy III. It is gained in the Eureka in the original, while it is gained from the Earth Crystal in the DS and iOS versions. Sages are highly adept mages who have mastered all levels of the Black and White arts. While they have numerous techniques at their disposal, their MP is limited compared to those spell casters who are more specialized. The Sage is considered to be a powered-up version of the Red Mage job.
The Sage has the ability to cast every magic in the game, as well as the high level Summon magic, making them a real threat. MP growth is higher than the Shaman, Warlock, and Summoner, so the Sage effectively makes those classes obsolete.
In Onion Knight's EX Mode, he utilizes the Sage Job class when using magical attacks. If his EX Burst is activated from a magical HP attack, the Onion Knight will use Holy and Meteor, or just Meteor if the player fails to select Holy. These spells are the most powerful of the Black and White Magic available in the game.