Ninja Gaiden Dragon Sword Codes -

Completion bonuses:
Successfully complete all chapters to unlock the following bonuses.

The "Prizes" option. This option allows you to view intermission sequences, letters, and character files that were found during your game session. Most are unlocked during game play by shooting the birds that appear when you use the microphone when a bird sound is heard.
The Hard difficulty setting. 

Muramasa's prize shop:
Successfully complete the game under the Normal difficulty setting.

The Way Of Kunoichi difficulty:
Select the Normal or Hard difficulty setting. Survive the fight with Ryu and defeat the dragon Boss to unlock The Way Of Kunoichi difficulty setting when a new game session is started. In this mode you will play as Momiji through the entire game.

Master Ninja difficulty:
Successfully complete the game under the Hard (Head Ninja) difficulty setting.

Birthday greeting:
Set the system date to your birthday. When the game is started you will hear a special "Happy Birthday" greeting when you tap the option to start the game.