The codes in the game allow you to gain invincility, Infinite Shurikens, and Bonus Points.

Code - Effect
Complete a level without throwing any shurikens - 30000 Points
Shurikens = 0, Sounds = Shuriken, then Highlight Shurikens - Infinite Shurikens
He runs, Japonesque, shinboi walk, sakura, getufu - Invincibility