Small update:
The movie's theme song will be "Unmei no Shizuku ~Destiny's Star~" (「運命のしずく~Destiny's Star~」- Shizuku translates to something like "drop (of water)"? Weird) by a group called GIRL NEXT DOOR.
Exciting, I know.
There are a couple samples of their past work . It's your basic J-pop fluff, which means I'll probably dig it because I have a weakness for Asian fluff-pop of questionable quality. Don't judge me. On the upside, it looks like they compose the vast majority of their songs so at least they're not just some studio mouthpiece.
The only thing that's really important here though, in my humble opinion, is that this means a trailer is probably imminent, given that they usually feature the theme song in the trailer.
Source:
http://m-78.jp/room78/zerothemovie.html