A story about a miracle, involving Fumika, a quiet but hard working girl who wears a uniform of a mail carrier, and her talkative staff and partner Mayama. The Shigofumi is a posthumous letter, the last resort of relaying a deceased person's last message to his or her loved ones: family, friends, and significant other.
Shigofumi primarily centers around a young-looking girl named Fumika who works as a mail carrier to deliver "after death letters" (死後文 ,shigofumi?). These letters are written by people after they die and are delivered to the person the letter is addressed to in the living world. The letters contain things that the now-deceased could not say while they were alive, such as things they wanted to say before they died, or even to inform others about who killed them in the case of a murder. Accompanying Fumika is her talking staff Kanaka which can also float of its own accord and likes to be treated as if "she" were a human. In contrast to Fumika who is quiet and serious about her job, Kanaka is loud and boisterous. The story follows Fumika and Kanaka as they interact with the living via the shigofumi. Shigofumi mail carriers are assigned a specific area that they deliver letters to, just like a normal mail carrier. When they are not delivering letters from the dead, they are in another realm called Shigo. The mail carriers are usually now-dead humans who do not age, and take on the appearance of just before they died, but Fumika does age, signifying that she is not dead yet.