After buying the Bottled Faerie, hop back in your airship and head to the city of Gaia (which is west and a little north of the Caravan). As soon as you enter the city, the Faerie will be released from its bottle and fly off. Now it’s time to find where it went. You should head west, past all the shops, north, past the Inn, then east and into the woods. If you follow the path, you will soon come to a lake where the Faerie will be waiting.
Approach the lake and talk to the Faerie. She will recognize that you were the ones that rescued her, apologize for “running” off, and offer to retrieve Oxyale from the bottom of the lake. Since Oxyale allows you to breathe underwater, it will be indispensable when we reach the Sunken Shrine.
After obtaining the Oxyale, return to your airship and return once again to Onrac. The Sunken Shrine awaits!