The Dragon Sword is a sword carved out of a dragons fang and was used by the ancient warriors of the Dragon Lineage to slay the Black Dragon. It has been passed down from generation to generation in the Hayabusa Ninja Clan and in the events on the Ninja Gaiden games this sword is in the possession of Ryu Hayabusa of the Hayabusa Ninja Clan.
Ninja Gaiden Black
In Ninja Gaiden for the Xbox (as well as remakes Ninja Gaiden Black and Ninja Gaiden Sigma) the Dragon Sword is the starting primary weapon for the player(Ryu Hayabusa). It is the most well rounded weapon in the game having no serious weaknesses and many players preffered to play through the game using the Dragon Sword almost exclusively. The Dragon Sword can be upgraded at Muramassa's Shop to increase the amount of damage it does to foes and unlock new moves. Later in the game the player receives the Dragon's Eye, a jewel carved out of a dragon's eye. After obtaining the Dragon's Eye, the Dragon Sword becomes even more powerful, doing more damage and unlocking new moves.
In Ninja Gaiden II for the Xbox 360 the Dragon's Sword serves mainly the same purpose as it did in the first game. It is once again the starting primary weapon and it is also once again the preffered weapon of most players for most sittuation. In Ninja Gaiden Dragon Sword, a spin-off created exclusively for the Nintendo DS, the Dragon sword is not only the starting and primary weapon of that game, but also that game's only primary weapon.