Tennis no Oji-Sama: Driving Smash! Side Genius

From the main game menu (i.e., after you press start but before you load or begin a new game) select the last option in the list. You should now have six options. Pick the one on the bottom right, and you'll be in the password entry screen. Type in the password you want, and then either press start, or tap the red button at the bottom right of the touch screen.

I can't take credit for these passwords, they were posted on the message board by pyonri.