Infinite DP
As the game begins, you'll be presented with a tutorial that explains how you can use your weapons. As the tutorial concludes, you'll need to fight some enemies. As you battle them, work on building up a high combo count. Once the enemies all have been vanquished, watch the screen for the indicator that your progress has been saved. Once that circle vanishes, you can bring up the pause menu and choose the option to restart the chapter. You'll be able to fight the enemies again, for additional DP, and you can repeat the process as often as you like until you have all of the upgrades and weapons you want.