A sea monster known for its voracious appetite has made an appearance... You must restore peace to the oceans!
This errand is available after completing the main story.
Your target is swimming around the Spindle, so since it's in the water, you will need the Sea Cow once again. Depart from the south beach of Hamelin, then head east and north around Autumnia until you spot the Lone Shark. Strangely enough, he's weak to Fire, so equip those Blazing Blades you got in Yule and light him up, using your familiars' fire tricks as well. He's quite a bit more dangerous than the last few bounties, so keep an eye on your HP throughout the battle, as it'll go from full to empty in a matter of seconds.
Defeat it and you'll complete the bounty hunt, return to the Swift Solutions to claim your reward.