All Shu generals:
Press WHITE, BLACK, X, Y, WHITE, R, L, BLACK at the main menu.

Opening Edit option:
Press X, BLACK, Y, WHITE, L, R, WHITE, WEISS at the main menu.

BGM Test option:
Press L, WHITE, Y, R, WHITE, BLACK, X, Y at the main menu.

In-game reset:
Press START + BACK during game play.
(This only works in certain screens)

Alternate costumes:
Press A or X when selecting a character to choose between two costume colors.

Bonus FMV sequence:
  All of the people from the gray army dancing:
  Highlight the "Replay" option at the "Opening Edit" screen, then hold L + R
  and press A.

  Zhu Rong singing:
  Highlight the "Replay" option at the "Opening Edit" screen, then hold BLACK +
  WHITE and press A.