Pause during the game and enter the following codes: 

Code   -   Effect 

Fill Kuji Meter:
Hold R + L then press Left, Left, Left, Right, X 

Get One Kanji:
Hold R + L then press Left, Left, Left, Right, X 

Score +=100:
Hold White + Black then press Right, Right, Right, Left 

Offensive Power x5:
Hold R + White then press Up, Down, Up, Down, then release R and White and press X, X, X 

Restore Health:
Press Up, Down, Up, Down, X, X, X 

Show Score:
Press Right, Right, Right, Left 

Unlock Special Move/Ability:
Hold R + Black then press Up, Up, Down, Down, then release R and Black and press X, X, Left Trigger.

Elevator Glitch:
In any level with a building that has more than one floor, like godah castle, you can easily bypass the entire first (or even second) floor. Use the cling to ceiling technique to cling to the ceiling. While on the ceiling select the grappling hook and press Y to go to the second floor.

Item Select Screen Cheats:
Enter the following at the Item Select Screen: 

Effect   -   Code 

Increase Ninja Items:
Hold R + L and press Up, Left, Down, Right, X, X, X 

Unlock All Ninja Items:
Hold R + L then press Up, Down, Up, Down, X, X, X, Left, Right, Left, Right, X, X, X 


Mission Select Cheats
Enter the following at the Mission Select Screen: 

Effect - Code 

Unlock All Layouts: Press R3, L3, L, R, White, Black
Unlock All Missions: Press White, White, L, R, Right, X, L3, R3 


Title Screen Cheats
Enter the following at the Title Screen: 

Effect - Code 

Unlock B-Side:
Hold L + R then press X, X, Up, X, X, Left, X, X, Right, X, X 

Unlock Through the Portal Bonus Mission:
Press White, Up, Black, Down, L, R, Left 

Unlock All Characters:
Hold White + Black and press Up, Right, Left, Down, release White and Black and press L + R 

Unlock B-Side:
Get at least Expert Ninja rankings on all of Rikmaru and Ayame's missions and Professional rankings on Tesshu's missions. 

Unlock Ninja Dog for Multiplayer Mode:
Get Grand Master rankings on all of Ayame's missions.