There's a lot of mention of some other recent related films, but only one person mentioned Shinkai's first movie, Voices of a Distant Star. It has many of the same themes (because all his movies do).

What's amazing about it is that he did pretty much the whole thing himself. The writing, the art--even the acting originally, but he did get professionals to redo it for the public release. Despite being pretty much a one-man project, it was still one of the most beautiful films when it came out (and still holds up). It's just incredible to think of how much he personally did for that movie. It's only like 30 minutes long, but still. After seeing that, I was certain Shinkai would be untouchable as an anime director, and I think that holds up. He's delivered the same quality consistently.