This is story related, can't be missed
It's for killing the first boss, which is fairly easy. Here are some tips though:
Try to find the secret breakable walls on the ship that hide HP and MP ups
Try to learn the summon shard from the ghost enemy and use it a lot during the battle
Try to get the helmet drop from the dullahammers and equip it
Get the Great sword from the chest in the vertical room on the far right and equip it as it allows you to damage the boss even when they move to the side of the ship
Try to find the country dress and equip it
Try to find the rusted ring and equip it
Try to find the tattered scarf and equip it
Try to be at least level 5