If you want to unlock the following features in the game enter the corresponding code without the quotes as a password.

Unlockable Bonus Stages:
Enter the code 'DAM ATA MAQ'.

Unlock Bonus Exhibition Mode Boxers:
Enter the code 'NEL SAZ UMA'.

Unlock Lunsaku Paudy, Junichi Hotta and Hiroshi Yamanaka:
Enter the code 'ALL *ST ARS'.

Unlock Original Kamogawa, Nekota and Hama in Exhibition Mode:
Enter the code 'MRS AND MAN'.

Unlock Broccoman in Exhibition Mode:
Enter the code 'BRC MAN EXH'.

Unlock Date vs. Ramirez Match in Story Mode:
Enter the code 'DAT EVS RMZ'.

Unlock Takamura vs. Yajima Match in Story Mode:
Enter the code 'ASA CT3 CLR'.