Shigofumi (2008)

Shigofumi are letters from the dead. Those who are dead and still have unfinished business can send an after-death-letter, yet, not any dead person is allowed to do so. These letters are delivered by the supernatural mail carriers, who once, just like their recipients, were humans. They now do not age and cannot be killed. Fumika, the main heroine of the series, is, perhaps, the most competent mail carrier, and sometimes it seems nothing can disturb her work, even a troublesome recipient. However, unlike her colleagues, Fumika, for some reason, continues to age, and on one of the Fumika's delivery missions, she meets a high school student, who knows her. It appears that in addition to the fact that Fumika is now an entity no human can comprehend, she has many mysteries behind her persona that are, little by little, discovered by Fumika and her closest friends.