Ikaruga

Chain meter:
Press Z during game play to display a chain meter under the chain status.
wruesch.

Full pause screen:
Press Start to pause game play, then hold X + Y.

Additional credits:
You will start the game with three credits and earn one for every hour of play to a maximum of nine credits (six hours). Free Play mode is unlocked after seven hours.
ikonos and bluberry.

Gallery 1 option:
Successfully complete trial mode without using any continues to unlock the "Gallery 1" option at the "Appendix" menu. Alternately, accumulate at least five hours of total game play.
wruesch.

Gallery 2 option:
Successfully complete the game under any difficulty setting to unlock the "Gallery 2" option at the "Appendix" menu. Alternately, accumulate at least ten hours of total game play.
wruesch.

Sound test option:
Successfully complete the game under the easy difficulty setting without using any continues to unlock the "Sound Test" option at the "Appendix" menu. Alternately, accumulate at least fifteen hours of total game play.
wruesch.

Game mode option:
Successfully complete the game under the normal difficulty setting without using any continues to unlock the "Game Mode" option at the "Appendix" menu. Alternately, accumulate at least twenty hours of total game play.
wruesch.

Control two players at once:
Note: This trick requires two Wavebird controllers. Set the receivers on the same channel and use one Wavebird on the same channel. You can then control two players at the same time. Set them side to side (horizontal) or (vertical) above each other by pushing them to the edges of your screen. If one gets wasted, you can quickly change color so you will have one black and the other white.
BlueWhistler3.

Increase score permanently:
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.
bluberry.

Dot Eater rank:
Do not fire the Ikaruga at all during a level. You must dodge or get hit by enemies and complete the level.
wruesch.

Alternate demos:
Go into the display options and change the view to one of the following settings before watching a demo. Depending on the screen type, different tactics will be shown during the demo.
wruesch.

Horizontal 1: Beginning tactics.
Horiztonal 2: More advanced tactics.
Horizontal 3: Advanced or Dot Eater tactics.
Vertical 1 or 2: Increased difficulties.

Hint: Unlock practice levels faster:
If you are having trouble getting to a chapter with one credit to unlock it in practice mode, pause game play when you are about to lose your last life. Then, press Start on controller two and use that controller to get to the chapter you wish to unlock. You must not use any continues after that.
khaascp.