While playing the game, press Up(2), Down(2), Left, Right, Left, Right, X, Circle. You can play a shooter mini-game on the in-game map at the top right corner of the screen. Note: This feature is available in the Japanese version of the game.
Successfully complete the game and save to unlock Keith as a playable character, Hard mode, Splatter mode, and New Game+ mode. Load your cleared game in New Game+ mode to start with all Combo Chips, Boosters, and stats from your previous game.