Need help figuring out the name of an anime movie?

So there was an anime movie that I've actually seen a few times and really like it every time I watched it. However, I can't remember the name. The movie was about a boy that lives in a village overrun by the forest and the people have learned to live along if not under the forest. The boy then finds a girl when he was stealing clean water. The girl was frozen or something from a past that was super technological and that didn't have to deal with the forest. The girl ends up going with another person from her time and they activate a giant moving building that was programmed to destroy the forest and everything in its way so that it could rebuild the old world. Oh, also the plants were overrun because of some impatient guy's experiments and he destroyed the moon and the girl had this funky necklace thingy that worked almost like a computer and cell phone.