Mushishi

Are mushi insects, parasites, plants, viruses, or nature spirits? Described as "neither good nor evil, they are life in its purest form. An unseen river shaping the path of man, through their presence our life is changed." No one seems to know much about their origins, except that they've been around since the beginning of time.
Possibly set in Meiji/late 19th century Japan, Mushishi is a series of related, yet separate short stories featuring Ginko, a mushishi. A mushishi or "mushi master" is a cross between a researcher/scholar/doctor/shaman who travels across the countryside searching for mushi in their many forms. Ginko wanders from town to town to find people, young and old who are affected by the mushi. He offers explanations, sometimes medication or direct intervention to try to cure the afflicted of their mushi-related problems. [Source: manga.about.com]