Question: I was thinking of writing a book with a POV that is not classified among the three that are commonly known. It is a fantasy novel, where the entire story (except prologue) is a history of the fantasy world as narrated by a certain character. My question is: do you think that such a novel is viable?Answer:
Certainly it could be viable.
What you are describing could be either:
1. A character narrator: that is, the story is narrated by a minor character in the story world. Such a narrator may occasionally bring him/herself into the story, referring to himself as "I" and the reader as "you." Otherwise, the book would be told in third person, past tense. The key to such a book is that the narrator should be someone who could reasonably be expected to know about the events being described.
2. Another, rarer approach would be to write the book using a fictional character as a pseudonym. In other words, your prologue would explain that what follows is a work of biography, history, or creative nonfiction, penned by a historian from some other world, that perhaps was discovered or obtained under mysterious circumstances. In this case, the reader assumes that the character can describe the events of the story because he/she has researched them. Again, this would probably be written in third person, past tense.
Of course, what makes such narrators interesting is that they may be unreliable. They may make false inferences, lie, or spin the facts a certain way.