Some time between Meiji and Taisho period... A mother and son walk through heavy rain. The son, Yoki, sees strange, iridescent creatures float from the mountainside and then disappear. He does not yet know such creatures are called "Mushi" and can not be seen by ordinary men. Suddenly, there is a landslide and Yoki's mother is swallowed by the flood. A Mushi-shi woman named Nui finds the child, who miraculously survived, and takes him home with her...
Some years later, we meet Yoki again as an adult. Having lost his memory in an incident he can not recall, he is now called "Ginko". He is a "Mushi-Shi," one who studies the Mushi he could see as a child and protects ordinary men from the illnesses that they inflict. He travels alone through the thick mountain snow, looking for a night's lodging. We see that his hair is white like the snow and one of his eyes is now missing...