Unlock all Characters
At the Title Screen press:
L1, R2, L2, R1, Right, Left, L3, R3

Unlock the Demo Level
At the ''Start Screen'' press:
Up, Down, Right, Left, X, X, X

You will now be able to play the level that was available on the free Demo disc prior to the game's release.

Increase Items
At the Item Selection Screen hold R2 + L2 while pressing:
Square, Square, Square, Up, Left, Down, Right

Unlock All Missions
At the Mission Selection Screen press:
L1, R1, L2, R2, Right, Square, L3, R3

Unlock Bonus Stage
At the Title Screen press:
L1, Up, R1, Down, L2, Right, R2, Left

Unlock all Items
At the Item Selection screen hold R1 + L1 while pressing:
Up, Square, Square, Left, Square, Square, Down, Square, Square, Right, Square, Square.

Unlock All Layouts
At the Mission Selection Screen press:
R3, L3, R2, L2, R1, L1

Restore Health
Pause game and then press:
Up, down, Right, Left, Square, Square, Square

Display abilities
Hold  L1,L2,up,up,down,down and release L1,L2, and press R1,R2

Unlock all abilities
Hold L1,L2,up,up,down,down,release L1,L2,press box x2,R1,R2,

Cheats
Get All Missions
Go to the mission select screen and press L1, R1, L2, R2, Right, Square, L3, R3

Get All Characters
Go to the main title screen and press L1, R2, L2, R1, Right, Left, L3, R3

Get All Mission Layouts
Go to the mission select screen and press R3, L3, R2, L2, R1, L1

Get All Items
Go to the item select screen and HOLD R1 + L1 and press Up, Square, Square, Left, Square, Square, Down, Square, Square, Right, Square, Square

Get More Items
Go to the item select screen and HOLD R1 + L1 and press Square, Square, Square, Up, Left, Down, Right

Increase amount of ninja items (10 more)
At item select screen hold R2 and L2 and press Square, Square, Square, Up, Left, Down, Right.

Get Extra Level (Rikimarus Secret Level)
Go to the main title screen and press L1, Up, R1, Down, L2, Right, R2, Left

Get Hidden Level
Go to the main title screen and press Up, Down, Right, Left, X, X, X

Get More health
During gameplay pause and press Up, Down, Right, Left, Square, Square, Square