Read below if you want a mini walkthrough about it. ;p
After you get the Airship,You can fly it near the Citadel Of Trials(since there is no place to land right next to it.) When you go through the Citadel of Trails and get to the boss and beat him,open the chest in the room to get the Rats Tail! Now You just gotta find Bahamut in the Dragon Caves(on the chain of Islands South West of the Citadel of Trails.) and give it to him.Then your people get to change classes. Yay!
// On the other hand, the Black Belt and the Thief get much tougher. They usually arent that much use in a scrap until you upgrade them. You wonldn’t need to buy weapons for your Black Belt after this either. ~
// PuRiKaH ~
He must like rat tails. :O
*Neglects to mention that the replies are moot seeing as he did this a couple of days before the first one, but thanks you all anyway.* 🙂