A Fox orb is an orb that is the origin of a nine-tail's power.
Foxes create these orbs through training and they are a "cohesive concentration of their spirit". Foxes with less than nine-tails cannot obtain this orb.
A fox orb is blue and emits a blue-ish energy. If swallowed by a human, it gets rid of all disease, allows long life and gives unthinkable power. Through training, a human can harness its power.
Banya's Orb Edit
Although he is a nine-tails, Banya's orb is in the possession of Bong-Hwang, the scroll contractor, which renders Banya weak and incapable of fighting other nine-tails. Bong-Hwang promised that in one thousand years, after Banya has rid himself of sin, he will return Banya's orb. However, according to both Ajussi and Banya, the return of the reincarnation, Bub-Woon, is necessary for Banya to get his orb back.
By retrieving the orb before a contract is made between the Medium he is protecting and the Gods, Banya says that he can become free of the scroll, regardless of which human is to become the Medium. Doing this may free him from the Gods.
For some reason, Ajussi finds this plan quite horrifying and unbelievable, also being doubtful in the chances of its success.
However, Banya has stated that the results will only be clear once it happens, and the Gods having been sending warnings to So-Yoon to become a Medium (this is the reason why many strange things have been happening around her). According to Banya, she maybe the last human he protects.
Bub-Woon swallowed Hwa-Yeon's orb upon her death. This enraged Banya, who accused him of both theft and the death of his mother. After sealing Banya into a scroll, Bub-Woon dies and becomes a spirit. To ensure Banya would easily be able to find him, he had Ajussi seal his soul inside the orb.
He then entrusts this orb to Ajussi, who, about a thousand years later, gives it to Lee So-Yoon.
However, the baby was dying, and instinctively absorbed the orb's power, becoming the orb itself, thus preventing Bub-Woon from awakening and taking full control of her body. This prevented Banya from discovering So-Yoon as the reincarnation.
As a child, Ryo-Woon was given an orb to swallow by his father. It was then passed around by his father that Ryo-Woon was the reincarnation, a fact which Hyun-Ryung is determined to prove for herself. It is implied that this orb belongs to the previous Red Elder, who either died or disappeared years ago.
According to Hyun-Ryung, this lie was made up for Ryo-Woon's protection.