Original characters by Makoto Shinkai.
This movie is really interesting to me. It was first created to be a movie, however the author was told to write a light novel to go with it. The production of the light novel finished first, at the end of the light novel the author talks about how he didn't know which one is "better". Since the movie was not done yet he couldn't compare it. However, he did say that the "original" is movie, since it was the base for the light novel.
Personally, I haven't seen the movie, but I did read the light novel. I would recommend everyone to read it. Is a beautiful story, I love the twists and turns the movie takes, and it gives me chills just thinking about it.