Natsume's Book of Friends

Natsume meets a shrine god in the form of an elderly woman. He is forced to help her return a mirror to a youkai said to bring disaster. The youkai turns out to be Reiko, Natsume's grandmother, who the shrine god only mistook as a youkai. Reiko had lent out the mirror so that the shrine god could save the life of an old tree, but the two parted after Reiko learned that the elderly woman was a youkai.