On the continue screen (where it shows you the face of a Japanese girl), wait 1 minute and then, starting from Up, do a clockwise motion with the control pad. If done right, a sound will be heard. You now have 1 extra continue. To get 3 more continues, just wait 3 minutes or more on the same screen and then press Up 10 times. If done right, a sound will be heard.
At the main menu, press the following buttons:
At the password screen, enter the following Japanese characters. Format is Row #, Column #.