Zero Divide: The Final Conflict

Unlock Zulu and Xtal, then accumulate twelve more hours of game play.

Successfully complete the game under the normal or higher difficulty level.

Unlock Neco, then hold L + R while selecting Xtal's stage at the stage selection screen.

Enter the "Key Config" option and change all the buttons to "No Use". Use the "Test 2" option that appears to play a mini-game that involves hitting Neco's head with a hammer.