The following details are from an Idea Factory International press release:

First, the winds stopped. Then, birds vanished from the skies. Finally, the sun set…
And an eternal night fell upon the world. The reason was quickly identified. It was a story told of in legends. The world had ceased hundreds of years ago as well. But there was a legendary mage who had managed to restart it.

Thus, elders gathered capable young Machina Mages from around the world. They sent them to the legendary city: Machina City, Southern Cross. You must restart the world, and bring an end to this eternal night. That is your mission, and your destiny. Now, go forth on your journey. Go, Estra!