Sega have highlighted one of the major differences between Hatsune Miku: Project Diva and Hatsune Miku and Future Friends: Project Mirai on the series blog. The way character selection worked in Project Diva, you could choose different Vocaloids to dance to each song, but the singer’s voice would remain the same, regardless.
In Project Mirai, in the case of certain songs, choosing a different character will make them sing the song instead of the original Vocaloid. Another — albeit smaller — difference is that outfits in Project Mirai are called “costumes” rather than “modules”.
You can see five of these above. The four on the left are for the song “Tricolor Airline,” while the one on the right is “Daughter of Evil”. Speaking of which, six songs have been confirmed to be in the game so far. Of these, we have screenshots of three:
Trilcolor Airline (artist: Atsuzou-kun):
Daughter of Evil (artist: Mothy):
LOL -Lots of Laugh- (artist: Ken and Endcape):
Tricolor Airline is one of the songs with different voice versions. While the original is sung by Miku, you could have Luka, Rin or Meiko sing it instead. The other three songs confirmed to be in the game so far are:
Watashi no Jikan (artist: Kuchibashi)
Piano Girl (artist: OSTER project)
Sing & Smile (artist: Re:nG)
Hatsune Miku and Future Friends: Project Mirai is slated for release on March 8th in Japan for the Nintendo 3DS. The game also has augmented reality features, such as AR concerts of which you can take pictures.