Instructions
Complete the game once.
Recruit a non-playable character that is the same class as your main character. The class of your character will depend on how you played the game.
Complete missions with the non-playable character until their relationship status says "Friend." Upgrade the character to the next job in his or her class.
Go to your class's guild and accept the quest from the non-playable character in the corner of the room.
Complete the quest. The quest will be different for each class. Return to the guild once you've completed the quest and talk to the non-playable character again.
Open the skill menu and look at your class. The ultimate skill will be unlocked for your class.