Short answers, pulled from the story.
The Fabula Nova Crystallis Final Fantasy series is a conceptual framework created by Square Enix in 2006 to unify disparate projects under a shared theological and philosophical umbrella. It features a common set of deities, crystals, and cosmic forces that are interpreted differently by each development team. The project was designed to create a sprawling mythos that would eventually spawn seven distinct games across multiple platforms.
Final Fantasy XIII was released in Japan on the 1st of December 2009 as a PlayStation 3 exclusive. It was later expanded to the Xbox 360 in March 2010 and ported to Windows in 2014 and 2015. The game became the flagship title of the series and the most commercially successful entry in the franchise's history.
Scenario writer Kazushige Nojima created the mythology for the Fabula Nova Crystallis Final Fantasy series after spending years researching Greek and Norse mythology. Nojima crafted a universe where gods, humans, and crystals existed in a fragile, often tragic balance. His vision allowed directors like Tetsuya Nomura and Motomu Toriyama to tell their own stories without being shackled to a single plotline.
The god Bhunivelze seized control of the mortal world by killing his mother, the creator goddess Etro, who vanishes into the Unseen Realm. Bhunivelze then created three new deities to search for the gate to the Unseen Realm, with the first deity Lindzei tasked with terraforming the world. Etro later gave humans pieces of chaos that became their hearts to maintain the balance between the worlds.
Final Fantasy Type-0 was released in Japan on the 1st of October 2011 for the PlayStation Portable. The game was originally titled Agito XIII and was later remastered as Type-0 HD, released worldwide in March 2015. It was co-developed by mobile game developer Tayutau K. K. and featured a multiplayer option where online players could take control of characters during the majority of the game.
The three games in the Final Fantasy XIII trilogy collectively sold 11 million units worldwide. The series included Final Fantasy XIII, Final Fantasy XIII-2, and Lightning Returns: Final Fantasy XIII. These titles expanded the world of Cocoon and Gran Pulse and introduced new mechanics such as nonlinear storytelling and open-world exploration.