When you load a previously beaten file you will be given a message. One part will say that you can now go to a place called Mysteria Ruins. It is located north of your starting point. The other part of the message will say that your levels are the same as well that you can use all the characters in random battles.
After you beat the game, you can go to the "Extras" section and look at the dialogue from the chapters, look at the character profiles, look at all the pictures from the game, and listen to SFX, music, and character voices from the game.