| I will have my revenge... against this world... against chaos...
— Fog Ship Guide
The Eternal City is clearly a victim of urban decay.
The Fog Ship Guide is a mysterious being from a parallel world. Filled with bitterness for unknown reasons, they seek the power of the 27 True Runes to enact revenge on this world.
While they have the appearance of an enormous monster, this is a magical shape that has no true substance, much like their vessel, the Fog Ship. The Guide's plan was to invite True Rune bearers to the Fog Ship where they would then take their power for their own.
Ted, who bore the Rune of Life and Death, was one such person but as he wanted to escape the curse of the "Soul Eater", boarded the ship voluntarily. During the Island Liberation War, the Guide would attempt to persuade the the leader of the Headquarters Ship to give up his Rune of Punishment but the leader instead convinced Ted to reclaim his rune, the Fog Ship Guide would turn on Ted and his newfound allies and attacked.
The Fog Ship Guide has extremely potent battle magic and proved to be a formidable foe. However, when Leknaat appeared, she was able to dispatch the being easily, returning it, cryptically, to its "Eternal City".