Ninja Gaiden Sigma Plus is a port of Ninja Gaiden Sigma for the PlayStation Vita released in North America and Europe on February 22, 2012.
Like Ninja Gaiden Black's "Ninja Dog" mode, Sigma Plus features an easier difficulty called "Hero" mode, making it more accessible to casual gamers. It also takes advantage of the additional features that the Vita offers, including gyroscopic first-person aiming (by tilting the PlayStation Vita, the player can adjust the camera angle in first-person viewing modes), back touchpad controls (tapping symbols using the rear touchpad will allow Ryu to boost the power of his Ninpo), touch screen controls (players can go into first-person mode by tapping the touch screen). In addition, Ninja Gaiden Sigma Plus offers new sets of accessories that Ryu and Rachel can equip.
Source: Wikipedia, "[en.wikipedia.org/wiki/Ninja_Gaiden_%282004_video_game%29%23Ninja_Gaiden_Sigma_Plus Ninja Gaiden (2004 video game)]", available under the CC-BY-SA License.