Team Ninja brought over Ninja Gaiden Sigma over to PlayStation Vita when the system launched this past February, and soon enough they'll be bringing over the sequel as well. Dubbed Ninja Gaiden Sigma 2 Plus (long enough for ya?), it was recently confirmed by studio head Yosuke Hayashi at Tokyo Game Show.
As of now, no further details are known, except to say it will hit early 2013.
Sigma Plus fared reasonably well in reviews, with critics noting it didn't offer much new, but was more or less the same great game as before, but portable and with new controls.