Nui is a Mushishi and the narrator of the anime series. Her voice can be heard in many episodes.

Nui's appearance is very similar to the series' protagonist [Ginko](https://anilist.co/character/425/Ginko). Due to her exposure to the Ginko Mushi, she has white hair and only her left eye (which has turned green). She is tall and usually wears a dark kimono. Since she doesn't have her right eye, she keeps it shut. Nui's appearance was different before being exposed to the Ginko, she had long, black hair, dark eyes, and wore a brighter kimono. Similar to Ginko, she smokes Mushi-Tobacco to keep Mushi away.

Nui is a Mushishi from an isolated yet beautiful village in the mountains. Due to her tendency to attract Mushi she rarely stayed in her village and often used to travel from place to place driving Mushi away. She still often used to visit her parents, friends, and her husband and child.

Due to her research on the Ginko, she was constantly exposed to its light and that changed her appearance. One day, she found an injured boy named Yoki in the woods who had lost his mother in a landslide. She tended to his wounds and explained to him the nature of Tokoyami.

~!One day while returning from her travels, she learned from other villagers that her husband, parents, child, and her friends had disappeared into the mountains. While searching for them she found out that there were Tokoyami living in a pond.

Once she realized that her loved ones were turned into Tokoyami by the Ginko, she then decided to live near the pond and studied the Tokoyami and the Ginko that lived within it. She used the fish in the pond to conduct her research only to find out that eventually all the fish exposed to the Ginko turn into Tokoyami.!~

~!She willingly exposed herself to the light of the Ginko and turned into Tokoyami. Before completely fading away, Yoki grabbed her hand and was also consumed by the Tokoyami. Within the Tokoyami, Nui's spirit guided Yoki and told him that in order to escape, he would have to sacrifice his memories and one of his eyes to the Ginko. The Ginko then awoke and consumed the rest of Nui.!~

(Source: Mushishi Wiki, edited)

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)

Some live in the deep darkness behind your eyelids. Some eat silence. Some thoughtlessly kill. Some simply drive men mad. They are known as mushi—creatures that came into being shortly after life emerged from the primordial ooze. They still exist parallel to our own lives and can only be seen by a select few. As a mushishi, Ginko is one of the few who are aware of their existense, and this young man with a sardonic smile roams from place to place with the knowledge and skill to aid those unwittingly affected by mushi.
 
(Source: Kodansha USA)
 
Note: Won the Excellence Prize for Manga at the 7th Japan Media Arts Festival in 2003 and the Kodansha Manga Award for General Manga in 2006.