Yesterday, while I was at school, I remembered an anime movie that I saw when I was younger. I wanted to look it up but I can't remember the name of the main character or the movie's name. I remember that the he got silver hair when he accepted the forest or something like that. His hair was brown at first. And there was a girl from the past... i think.. or maybe the future?

Please help me out if you know the movie's name and even this character's name.