In a city that is neither small nor big... There's a mountain that people avoid. The undeveloped mountain isn't protected with a green belt... Nor is it a site of environmental conservation... The avoided, prohibited forest... With the dismal atmosphere and the rumors that whisper about the spirits led it to be called... Spirit Mountain. On the mountain is a house... A famed house of mediums that show off their long, glorious heritage. Hence, it was once called Medium Mountain. But once a long time ago... They said a Ninetails lived there... And was known as the Fox Mountain. But 20 years later... A dark aura has covered this isolated place.
A Thousand Years Ninetails is about a young fifteen year old girl who lives on Spirit Mountain named Lee So-Yoon. She was born with very strong powers and has been able to see spirits since she was little. In her house there's a scroll which contains a Ninetailed Fox named Banya who is looking for the monk who stole his mother's orb (a small orb created from a fox gaining mastery of their powers and is affected by the good and bad deeds of the fox) and sealed him in the scroll. Every thousand years, the monk is said to be reincarnated, so at night, Banya goes searching for him (a spirit's powers are stronger during the night, according to Banya).
So-Yoon was born Into a family of mediums and was encouraged to receive a god (which she was told by her grandmother that it's like marrying a god) but refused because she doesn't want Banya to waste his time looking for the monk who sealed him to protect her. Banya's goal is to find his reincarnation and kill him after he releases him from the scroll (which So-Yoon doesn't know about the killing part) while So-Yoon's wants to help find him (at first) but at the same time, she doesn't want Banya to leave them. Banya has to protect So-Yoon because her powers attracts many bad spirits to her, and the two's relationship soon begins to become romantic as true identities become revealed.
- When the webtoon was first serialized, many people pointed out Banya's similarities to Inuyasha, from Inuyasha: A Feudal Fairytail, by fans. Later on, Giryang let it be known that Banya was a fox, and not a dog, like Inuyasha, and the controversy ended.