Description stolen from wiki:

The official Japanese website revealed a web novelization titled Final Fantasy XIII Episode Zero: Promise. It contains a series of short stories written by Jun Eishima, leading up to the events depicted in the actual game. The first story is called "Encounter", and it focuses on how Serah Farron became the first Gran Pulse l'Cie in Cocoon for a long time. The second story is called "Friends", and it focuses on Hope Estheim's life with his family and friends before his mother's death. The third story, "Family", focuses on Sazh Katzroy and his son, Dajh, detailing how Sazh came to own the Chocobo chick and how Dajh fell into the clutches of Sanctum.
Final Fantasy XIII Episode Zero: Promise is a series of web novellas written by Jun Eishima, depicting the thirteen days leading up to the events of Final Fantasy XIII. New chapters involving Snow, Fang, and Vanille were released in a published Light Novel.

The first part of the series, titled "Encounter", is about how Serah became a l'Cie and her relationship with Snow and her sister, Lightning.

The second part of the series, titled "Stranger", is about Fang and Vanille after they awake from their crystallized state, trying to adjust to Cocoon life, and their arrival to Euride.

Part three, titled "Treasure", is depicting the story of Sazh and his son Dajh on being a l'Cie.

Part four is titled "Search", is about Fang and Vanille after they are separated in the Euride Plant, though it's told from Fang's point of view. It is about Fang worrying about Vanille, meeting Cid Raines and Rygdea, and joining them in order to find Vanille.

Part five, titled "Friends". It is a small story about Hope, his friends, and family before his mother died.

Part six, titled "Present", is about Snow and Serah

The seventh and final part of the series is titled "Tomorrow"
Contains spoilers apparently but they all got translated into this blog:

http://dilly-shilly.blogspot.com/

Not broken English too, it feels like an actual novel. EDIT: Not all; I misunderstood, but it's a work in progress but he seems to be working fast maybe.

I've not played the game yet as I am not anywhere "stable" but after watching some of the trailers to get the faces and voices into my head I found these to be an interesting read. Thought I'd share it here since no one has mentioned it. I love this kinda stuff personally