Shin Megami Tensei IV, the upcoming role playing game by Atlus, is a game about samurai. The protagonist is a samurai, actually. That means you have two mandates: to take care of the demons (would this be an SMT game if that weren't the case?) and to keep the peace.
Also probably more than those two things, but hey. One thing at a time here; anything more will be revealed via plot twist while playing, I'm sure.
Oh, and, here's a cool new tidbit according to the YouTube description on this trailer: the game will have branching plot lines, along with the previously discussed StreetPass functionality. Sweet.