England is sealed inside the world of writing known as a book. As people began moving from Europe to the New World in the latter half of the fifteenth century, the non-humans took over England. In order to create a protected land for them, the gods and demons that led them cut England away from reality and sealed it inside the book they had made. The monsters, gods, demons, and heroes that had existed in reality until that point moved to that imaginary England and lived on as fictional beings...that is, as beings that only exist in the form of writing and words.

As a book, England has a cover known as heaven and a back cover known as hell. Between those are nine chapter title pages, the same number as there are orders of angels. From the moment you set foot in that foreign land, your own form and emotions are expressed in writing. Humans rarely have a chance to enter that space.

The name of that world of fiction and the title of that book is "Aerial City – London."

(From "The Lost World")

(Source: Baka-Tsuki)