If done correctly, the game will mock you for entering the overused code.
Hints
Unlock Bonuses
Iji has a host of content that can be unlocked through various means:
Alternate Outfit - Beat the game on Extreme or higher.
Enemy Information - Achieve the "Immortal" gameplay rank.
Play Hero 3D Menu Option - Beat the game on Hard or higher.
Sector Maps - Beat the game on Normal or higher.
Single Sector Play - Beat the game on Normal or higher.
Sound Test Menu Option - Beat the game on Normal or higher.
Sudden Death Sector - Beat the game on Hard or higher.
Turbo Mode - Beat the game on Ultimoral.
Weapon Information - Achieve the "Nanomaster" gameplay rank.
Reboot (Reset Stat Points)
At any time during the game (except during boss battles), press and hold [Down] and press [C], [C], [C], [Z] to "reboot" Iji's nanofield, resetting all stats (excluding jump and armor upgrades) and returning all spent points, at the cost of most of your ammo and health. You will also no longer regain health from upgrading your health stat for the remainder of the sector.