Pick any character then enter the versus mode and lose the match on purpose. Afterwards save the game then pick Charlotte on the second player controller to continue with. During the bonus phase ahead simply press start on the firt player controller and Charlotte will turn into Amakus.
At the Versus character select screen the player who wants to be Kuroko should use this code: Up, Down, Left, Up, Down, Right+A.
After the current match the game will reset.