End Game Save - New Game Plus
Successfully complete the game first. Then after the Credits, the game will take you to the Save/Load/Exit menu, select Save. On the main menu, select Load and load the end game save, you'll be starting the game from the beginning but you keep the money and the characters' EPs from the previous game, everything else will be reset.

Secret level in the Demo
After you have completed all the available missions in the demo, save your game (Make sure to do it after you complete the last mission). Then, load that save up and go to the mission list. Make sure the first mission is selected and press Up and X. You will then be taken to the Wanzer Shop, and, once done, will start the secret bonus level in the Demo