Gran Pulse is a deserted wilderness once populated by people and many great cities. In the modern era of Final Fantasy XIII, however, Pulse civilization has long been wiped out, with ruins of civilization being all that remains of its former human population. It has since become a world of pure wilderness infested with monsters. High in the sky above Pulse is Cocoon, a floating utopia constructed by fal'Cie meant to keep the human population safe from Pulse's dangers.
Final Fantasy XIII
In Final Fantasy XIII, Lightning and her party are forced to flee Cocoon and arrive on Pulse in search of the meaning behind their l'Cie focus. Pulse is also the former home of Fang and Vanille; two Pulse natives that had previously completed a focus as l'Cie and hibernated as crystal through the many years between the fall of Pulse civilization and the modern era.
Final Fantasy XIII-2
Pulse is the primary setting of Final Fantasy XIII-2. At the end of Final Fantasy XIII, Cocoon threatened to fall on the planet's surface, but as it fell, Fang and Vanille became a crystal pillar, hoisting Cocoon in the air to avert tragedy. The people of Cocoon migrated down to Pulse, where a new civilization was established.
Lightning Returns: Final Fantasy XIII
After Lightning fails in her task to protect the goddess Etro in Final Fantasy XIII-2, an influx of Chaos energy consumes Pulse over the course of five centuries, leaving very little of the world habitable. The last remnants of the world where humans still dwell is referred to as Nova Chrysalia. In Lightning Returns, Lightning is tasked with saving as many of Nova Chrysalia's remaining residents as she can before the world is destroyed and the god Bhunivelze creates a new world to replace it.