Once you have unlocked the final dungeon and have arrived in Loegres. Head back to Meirchio and you will learn that Kamoana has come down with a fever. You will end up going to Haria to get her medicine.
This quest will prevent teleporting to many places. Head back to Hellewas and sail to Yseult. At the exit towards the beach an NPC will alert you of a troll that has taken Haria. Head there and defeat the troll.
After defeating the troll head back to Meirchio and you will learn Kamoana has gone on a rampage in therion form. Medissa has lured her to Mt. Killaraus. Head there and a cutscene will play out. Once it is done the Quest will be complete.