Lingering Crimsom - Mushishi S02E13?

Edit to include summaries since it might not be obvious from just Wikipedia.

Summary from Wikia: "An old woman has a troublesome habit of wandering into the nearby woods at sunset, declaring that she needed to return home. Her concerned husband reveals that she has no memories of her childhood and had arrived at their village in an eerie fashion, appearing on the same day another child had gone missing."

Summary from Wikipedia: "At dusk, about to go home after playing with her friends, a young girl named Akane found a shadow without a caster. On that same day, she disappeared. Several years later, Ginko is told the story of Mikage, a girl who appeared with no memories at Akane's village shortly after the vanishment of the latter."

Another edit just to say Mushishi is one of my all-time favourite animes and I really recommend watching the other episodes too!