All Shinobi have a fundamental understanding of the history of the known continent, which was divided into six lands for as long as written history could be traced back to.
The land of fire, water, wind, earth and lightning had a long and bloody conflict for territory and resources for over a hundred years until the Shinobi system was invented in order to keep strong standing militaries without promoting unnecessary hostility to surrounding nations. This Shinobi system is on its way to hitting nearly two centuries of standing peace, with four to five kages in each nation having come and gone. During this time, a great deal of technological advances occurred, allowing a quality of life unimaged by the ancestors that had come and gone.
That is, until three great cataclysms hit the land of earth, wind and lightning, rendering them nearly lifeless and all survivors forced to immigrate to either of the two surviving civilizations.
Thirty years after, the ramifications of these events are still only uttered in secret, as the few rare survivors who were alive during the cataclysm claimed that the thunderstorm and hurricanes almost had a life of their own...

Ok, good basic background. Then what? Who would the characters of this story be? What kind of technology level are we talking about? What does the surviving great nina nations look like now? What about the smaller nations?

You have a good leg to stand on here, but in order to attract players you need some more information than just a background hook.