Unlock Expert Mode: At the 'How to Play' screen press Back, Forward, Back, Forward, Forward, Back, Forward, Back.
Unlock Yamazaki and Jin Twins: At the 'Character Selection' screen highlight the following characters in the listed order and press the X button once on each character. After each time you press X on a character you will hear a confirmation chime.
Terry, Hon Fu, Mai, Geese, Bob, Sokaku Mochizuki, Andy, France, Joe Higashi, Blue Mary.
If you have entered the code correctly Ryuji and the Jin twins will apprear on the 'Selection' screen.