The Mushi are neither plant nor animal, neither microbe nor fungus. They are more like primitive life forms. Their existence is so innocuous that we don't notice that they exist until they have manifested some mysterious phenomena. They do not exist to frighten people; they just are.
These are one-off stories about Ginko, the Mushishi, one who knows about the Mushi and who acts as a mediator between humans and Mushi. During his journey, he meets various people and Mushi.