How do I continue after finishing the main storyline of Final Fantasy XIII?

There is no way to go back to the main story are the beat the game. All you can really do is chill out and explore Gran Pulse and upgrade your stats and weapons. It's not too bad because many of the enemies there are stronger than the final boss in the game.

But if anyone out there knows a way to return to the main game story please tell.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.