You need to beat at least one character's story mode then Password mode will be unlocked.

Effect	Code
Belzebrute Y	WlCQtq4hNs
Cyber Lambda S	Zw71nVSJuL
Cyber Pegasus Lambda R	DZ4gjMA58V
Pegasus Omega M	bMJ4O7osHq
Pegasus Omega W	Po0OiV3Qny