Ninja Gaiden Sigma 2, also known as Ninja Gaiden Σ 2, is the redefined PlayStation 3 version of Ninja Gaiden II.
The game features three additional playable characters : Rachel, Ayane and Momiji (from Ninja Gaiden Dragon Sword). The game also features new large-scale bosses, an online co-op mode and Trophy support. It uses the same engine as Ninja Gaiden Sigma and features better graphics than the original XBOX360 version.
Source: Wikipedia, "http://en.wikipedia.org/wiki/Ninja_Gaiden_Sigma_2," available under the CC-BY-SA License.