Lightning Returns: Final Fantasy XIII Chronicle of Chaotic Era is the name of a cancelled prequel novel to Lightning Returns: Final Fantasy XIII by Benny Matsuyama.
The 256-page long book was to have stories set around characters such as Snow Villiers, Noel Kreiss, and Hope Estheim. As the title suggests, the book was to have been set within the five hundred years between the release of Chaos into the mortal realm and the arrival of the savior. The main focus of the book was to have been "a drama of people struggling against despair in a world eroded by Chaos".
On March 16th, 2014, Toriyama said during a Dengeki event that the novel will be published via the official website in segments although Square Enix is yet to make an official announcement. Later, in an interview, Daisuke Watanabe revealed that he conceived elements of Final Fantasy XIII: Reminiscence -tracer of memories- with help from Matsuyama, and that material from Chronicle of Chaotic Era was actually incorporated into the text.
The novella Final Fantasy XIII: Reminiscence -tracer of memories-, published between June and July 2014 via the official site, contains a reference to this unreleased novel: the folder Hope creates on the period between Final Fantasy XIII-2 and Lightning Returns: Final Fantasy XIII for the reporter Aoede is called "Chronicle of Chaotic Era". This alludes to the material from the cancelled novel being incorporated.