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 #.
At the main menu, press Left, Right, I, II, Left, Right, I, II. A sound will be heard if done right. Now, hit button 1 the same number of times of the stage you want to start in and then press Run.
At the main menu, press Left, Left, Right, Right, I, II, I, II. If done right, the Visual Test will start. Now, to cycle through each image, you have to press the following buttons: I, Left, Right, II, Up, Up, Left, II, Down, Right, II, I, Down, Up, Down, Run, II, I, Up, Run, I, Left, Right, Right, Up, Up, Up, Down, I, Left, Down, II, Run, Right, Down, Left, Right, I, Run. In addition, if you press Select at any time, you'll get a screen with a boat and an island.