5 Centimeters per Second: 12/24/15
5 Centimeters per Second by Makoto Shinkai is a two part manga about a friendship that could have been so much more but is allowed to peter out.
Tono Takaki and Shinohara Akari are best friends in grammar school and might even become a couple when they get older. Unfortunately that's not be because one of them moves. No matter of cajoling or begging can let them commute to a school on the train.
They try correspondence but shyness and other things get in the way, as they do. And so slowly but surely they grow apart. There's one last ditch effort to meet via train and everything hinges on it.
5 Centimeters per Second reminds me most of two books: Blankets by Craig Thompson and a picture book, You and Me by Susan Verde. One is directly about an intense relationship that falls apart after a long distance journey. The other is a what if, playing on all the ways their friendship could have ended before it even began.