To enable this feature hold the partner button during the character introduction sequence before the match begins.

The following characters become available when you clear Arcade mode the indicated amount of times and then purchased them at the shop when you have collected the specified amount of points.

Unlock Saki Omokane:
Clear Arcade mode 1 time and then purchase her for 1,000 points at the shop.

Unlock Hakushon Daimaou:
Clear Arcade mode 1 time and then purchase him for 1,000 points at the shop.

Unlock Ippatsuman:
Clear Arcade mode 3 times and then purchase him for 2,000 points at the shop.

Unlock Viewtiful Joe:
Clear Arcade mode 3 times and then purchase him for 2,000 points at the shop.

At the end of the game when the credits are rolling press A and the black background will change into a barebone platformer and you will be able to control Doronjo and her subordinates.