Beautiful. One of the best one-shots I've ever read.

This is a story about a little girl named Akino who went up to the mountain in the autumn with her father one day. When she went up to the mountain, Akino saw leaves from a tree that were BLUE. Even the tree itself was blue. She met a boy named Konoha, whose spirit lies within the tree. Akino continues to see him, but she can only see him in the autumn, for that is the only season he comes out.

As the story progresses, it shows Akino's growing affection towards Konoha and how she begins to hate the other seasons for she cannot she Konoha during those times.

This manga has a someone bittersweet ending, so be prepared.
But it's truly captivating and really worth a read.