I wpuld make the trailer something like, the mao in a cartoon kindo of way with a voice in the background saying few things "this is the shinobi world yadayada there was a conflict yadayada and now, ten years of peace after konoha was created yadayada" and as they speak, the map gets closer amd closer to kono, and as distance gets closer, transition slowly from cartoon to game view from the sky, closer and closer ending up inside of konoha academy, where the hokage or X high rank ninja is telling this story as a class or something.
Then someone asks "what about outside the village?" or something of the sort, then this person telling the tale would simply smile and some images of ingame jutsus, simple ones in the beggining, then more and more complex or more big in magnitude, ending in a scene like the time jiraiya, tsunade and orochimaru fought, with their summons out, then sudden cut and back to the smile "why don't you forst graduate and find out yourself?" or something similar expressing that think hahahahaha
About the music, i would put somwthing simple for the first part, like asian flute you know? All like Mist of Pandaria kind of vibe, slowly fading until reaching the classroom, and stopping with the question from the alumn, the something with more beat to it, since its with some fighting and skill, crescendo, crescendo, crescendo and sudden cut simultaneous the music and the images. Ending with a cool logo with "Shinobi Story, your story" more or less.
PD: Sorry for my bad english hahahahaha