Ninja Gaiden is a 2004 action-adventure video game developed by Team Ninja. It was the fifth original release in the Ninja Gaiden video game series and the first for the Xbox console. A second edition of the game, titled Ninja Gaiden Black, was released approximately eighteen months later, in September 2005. It is essentially a Director's Cut or Special Edition of the original Xbox release of Ninja Gaiden.

It features two new difficulty settings (Master Ninja & Ninja Dog), much of the content from both "Hurricane Packs" with the exception of the Intercept "parry", tweaked enemy placement in the extra difficulties, four new costumes, the original arcade version of Ninja Gaiden, a new mission mode with 50 short missions (including 5 from the previous "Hurricane Packs") involving scenarios not found in the core game itself, one longer and more challenging mission called "Eternal Legend" (unlocked after beating 40 of the missions), and several new in-game cutscenes.

Unlockables

Difficulty Levels
By completing these tasks, you can then unlock a different difficulty level for Ninja Gaiden Black.

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.

Master Ninja - Complete the game on Very Hard.

Ninja Dog - Die three times consecutively in Chapter 1, then accept the choices given to you.

Very Hard - Complete the game on Hard difficulty, or have a save file with the clear data of the Hurricane Pack 1

Golden Scarab Rewards In Very Hard Mode
Select the "TALK" option at Muramasa's shop to give him Golden Scarabs. He will keep track of how many you have turned in so far and reward you with items based upon your cumulative total.

Armlet of Fortune - 30 Scarabs

Dark Dragon Blade - 50 Scarabs

Jewel of the Demon Seal - 35 Scarabs

Jewel of the Demon Seal - 15 Scarabs

Jewel of the Demon Seal - 25 Scarabs

Plasma Saber Mk.II - 49 Scarabs

Spirit of the Devils - 20 Scarabs

Spirit of the Devils - 5 Scarabs

Spirit of the Devils - 45 Scarabs

The Art of the Ice Storm - 10 Scarabs

The Art of the Inazuma - 40 Scarabs

The Art of the Inferno - 1 Scarab

Unlockables - Costumes
Defeat the game in the following difficulties to unlock costumes:

DOA Throwback costume - Defeat Eternal Legends Mission

The Ashtar Ryu outfit (from the hurricane pack) - Defeat Ninja dog/ Normal

The Hotsuma Costume - Complete Hard Mode

The Ryuken (classic) Costume - Complete Very Hard Mode

Secrets

Hidden Windmill Shuriken
This secret can be found just outside of Han's bar. If you are lucky enough, a hint in the form of a pink Kunai scroll will tell you to look for a special weapon left behind in an alley that "only a Ninja can get to". You can find this "alley" right outside of Han's bar to the left. After defeating the ninjas outside, turn to the alleyway and look up. You will see a series of blue strips throughout the alleyway in which you can use to run back and forth about the alley. Do this, starting with the first strip just outside of the alley and then jump to the second and finally the third strip, all the while running along the wall. Once you hit the last strip, jump to the ledge right across from it. Here you will find the Windmill Shuriken embedded in the wall and an "X-box" symbol that revives your KI energy and your life. Once you've taken the shuriken you can continue with the mission with a new deadly weapon at your side. Good luck. Doesn't work in hard mode.

Play Japanese version of Arcade Ninja Gaiden
After unlocking the arcade Ninja Gaiden at the main menu, change both text and speech to Japanese and you will be able to play the arcade Ninja Gaiden in Japanese.

Here's a video of the Chapter 3 speedrun in Ninja Gaiden Black: