Magic Knight Rayearth

Note: This game is also titled Majikku Naito Reiaasu.

Invincibility:
Hold A + C + X and press Start when the phrase "Press Start" appears at the title screen. Fuu and Umi will be invincible when a new game is started.

Alternate introduction song:
Turn on the Saturn. After the Saturn logo appears, hold X + B + Z + L + R until the introduction starts. You will hear a different variation of the introduction song.
Information in this section was contributed by Jeremy Prusak.

Remove text from new game screen:
Hold Left and press X at the new game/continue game screen.

Hint: NiGHTS Into Dreams reference:
Upon arriving at Aeuria, The Sky Garden, from the entrance walk up the stairs and take a right. Continue to walk up. At the fountain, take a left and walk up the path just before the stairs. At the path's end, you will notice a strange object. Have Hikaru examine it and she will say, "What is this, anyway? Looks like that floating thing (Ideya Capture) from "NiGHTS".
Information in this section was contributed by Jeremy Prusak.