With the addition of Kaori into their party, Hajime and his friends make for Myu's hometown, the coastal city of Erisen. While crossing the Gruen Desert, they save a young Ankajian man, Bize, from a sandworm attack. Apparently, he was searching for a cure to the mysterious disease that has struck his people. His travels led him to conclude that a mineral known as stillrock held the key to saving his country, but it can only be found inside the Grand Gruen Volcano, a labyrinth far too dangerous for most. Hajime agrees to help Bize procure some, and the party begins their quest to conquer yet another labyrinth. But along the way, they meet a most unexpected foe...