Sky Pirate perhaps? With the appearance of airships in Eorzea increasing (although I will admit this is far-fetched), perhaps some group of enterprising pirates tries their hand at raiding with one, and the alliance in response is looking for adventurers to intervene. After reaching lv30 in Musketeer, you find yourself volunteered to be bait on a commercial airship, and after defeating the Sky Pirates, they agree to serve the alliance in return for amnesty, establishing a training school for combat in their way.