If you talk with the Chief Steward on your first airship flight you get the option to participate in a sidequest.

You get the item "Ann's Letter" and have to deliver it to her six sisters who are chief stewards on other airships throughout Ivalice.

You cannot finish this side quest until you can access the port of Balfonheim's Aerodome. If you complete the quest, you get the ring of renewal which gives you 6 defense, 5 magic resistance, and regeneration.