Mushishi

Neither good nor evil, they are life in its purest form. Vulgar and strange, they have inspired fear in humans since the dawn of time and have, over the ages, come to be known as "mushi." The stories of the Mushi and the people they affect are all linked together by a traveling Mushi-shi, or "Mushi Master," who seeks rare Mushi sightings and uses his shaman-like knowledge of Mushi to help the affected people.

What are the Mushi and what do they want?

(Source: Funimation)