Ikaruga Cheats

Finish the game using easy difficulty and don't
use any continues and this will be opened in the Appendix Menu. 
You can also get 15 hours of gameplay in to unlock it as well

Every time you continue, the last digit of your score goes up by one permanently. For example, if you continued once it is a "1", twice for a "2", etc. This is useful for gauging how much you have continued once the "Free Play" option has been unlocked.

Chain Meter:
Press Z during game-play to display a Chain Meter under the Chain Status.
Additional Credits:
To get additional credits accumulate at least 3 or 4 hours of total
game-play. Once you have accumulated 6 hours you should have about 9 credits from the start.
Gallery 1 Option:
Without using any continues successfully complete Trial mode to unlock the Gallery 1 option at the Appendix menu or accumulate at least 5 hours of total game-play.
Gallery 2 Option:
Complete the game successfully in any difficulty setting to unlock the
Gallery 2 option at the Appendix menu or accumulate at least 10 hours of total game-play.

Gallery 1-Play the game for 5 hours or complete the Trial Mode without continuing
Gallery 2-Play the game for 10 hours or clear the game on any difficulty setting.
Game Mode Option-Play the game for 20 hours or beat the game on Normal without continuing.
Sound Test-Play the game for 15 hours or beat the game on Easy without continuing.

Play the game for 15 hours or beat the game on Easy without continuing.

To unlock Sound Test, beat the game on Easy without continuing. Or, play the game for more than fifteen hours total. Sound Test will be available in the Appendix menu.