Hold the Arrows and press the [ ] button during the song selection mode.

When choosing the 3 songs for the non-stop mode, you should go to the song you want as your bonus song and do the high-speed code there(by holding the left and right button together). You can don't activate any thing, but you need to press the box out(by holding the left and right button) and exit from it.After that you can choose your 3 songs. If doing link, both players must do this code(for safety purpose. I don't wish people accusing me of my code not being able to work). For this code to work, you need to have a minimum of 100 combos during the first three songs.

When at the song selection screen,move to the song you want, then move your hands over the arrows as I written.Front,front/right,right,front,front/left,left. For safety, you could do this code a few times and wait for the timer to end. If not you can just press the start button. If done correctly you should be able to get Usao Kun. A character(The purple colour rabbit) used in Keyboard Mania.