Frontier begins with Raguna searching for a missing girl, Mist, who has moved to a new town because someone is calling to her in her dreams. Raguna moves into the town as well, living in the house next to her with a field. Then Raguna finds out that the whale island in the sky is in danger of falling on the town. Somehow Mist and another girl named Iris's fates are tied with the whale's. After going through some dungeons, he soon finds something peculiar is happening. (wiki)