Ninja Dog
Die three times consecutively in Chapter 1. Ayane will ask you, "Do you really give up the way of Shinobi?" Answer yes to begin Ninja Dog Mode.

Normal
Available from the beginning.

Hard
Complete the game on Ninja Dog or Normal difficulty. Or, have a save file on your hard drive where you completed the original Ninja Gaiden on Xbox.

Very Hard
Complete the game on Hard difficulty. Or, have a save file with the clear data of the Hurricane Pack 2

Master Ninja
Complete the game on Very Hard.

Mission
Complete the game with the difficulty level over Normal.

Movie Theater
Complete the game with any difficulty level.

Arcade Ninja Gaiden
Complete the game on Ninja Dog or Normal difficulty with the "Ninja Gaiden Arcade" item. Or, complete the game on Hard.

Coming Attractions
Play the game for over 1 hour.

New Missions
The first 10 Missions will be available from the start. Once you complete the first 5, and then 5 more will be unlocked. The rest follow in this pattern (five at a time) until all 50 have been unlocked.

Costumes

    * Normal: Available at the beginning.
    * Comic: Complete the game on Ninja Dog or Normal
    * Red Muffler: Complete the game on Hard.
    * Ryuken: Complete the game on Very Hard.
    * DOA: Complete "Special Mission." 

Play Ninja Gaiden (NES)
Collect all 50 Scarabs and turn them in to the shop to receive the Ninja Gaiden cartridge. Take this to Han's Bar and play it on the arcade cabinet.