The same song is used in the youtube trailer for this movie, though it's not in the film itself. I've been trying to figure out the track for a few days now with little to no luck.
I do agree though, it's a wonderful movie and something that everyone should go see. I was scoffing the first time I saw the trailer, thinking this was little more than a Japanese version of Alice in Wonderland. It really isn't, I would rather call it a tribute to the work of Hayao Miyazaki (I actually believe Teo is in part based off of the man himself.)
The storyline is pretty standard stuff, but that just doesn't matter when the coherent visual spectacles take over, metered out between scenes of powerful stillness and emotion. They really created quite an interesting world here and filled it with some very unique characters. I'm hoping for more OI films in the future.