While spending a vacation with her grandparents, Mayu, a Japanese first-grader, finds a mysterious mailbox in the forest near their house. She writes a letter and leaves it in the box. The next day she is surprised to find a letter addressed to her. She responds and a friendship develops between the two letter writers. But who could this mysterious friend be? Mayu discovers who he is, and discovers the joys of writing and receiving letters. And when the time comes to go back home, she and her forest friend find an unexpected way to exchange letters and to continue their friendship.
