Rods containing the souls of 9 foxes. Bestows incredible power.
The Fox Rods are a Dark Instrument used by the Dark Lord Ninetails, and take the appearence of nine bamboo flute tubes. They act as the key to her power, and without them she is rendered much weaker, the majority of her power unavailable for her to use. The Rods themselves manifest as Tube Foxes.
Prior to the events of the game, Ninetails would menace Nippon as the Dark Lord of Ryoshima Coast, this title to be given to her by Yami. However, during an attempt to lay seige to the Dragonian realm underneath the sea, a battle with King Wada as the Water Dragon led to the loss of the Rods, which the Dragon had seized from her grasp and swallowed, despite suffering major injuries. With such a dark and twisted mass of power lodged in his stomach, the Water Dragon fell into the grip of madness and caused havoc in the sea, wrecking ships and killing many. Weakened heavily, Ninetails killed the Priestess Rao of Ankoku Temple and posed as her in an attempt to get closer to Queen Himiko, so she could kill her before Himiko found the location of Oni Island.
Following the arrival of Amaterasu in Sei'an, 'Rao' (actually Ninetails) claims the Fox Rods to be a powerful holy instrument sought after by the Queen, and requests that the Sunken Ship be searched for them. However the Rods are not actually there. Later, the Fox Rods are found whilst searching inside the Water Dragon for the Dragon Orb. When the Orb is removed forcefully from the belly of the dragon, the eight Tube Foxes emerge and attack; and upon their defeat become the Fox Rods. Once Amaterasu exits the Dragon's mouth, she and Issun meet the spirit of King Wada, who explains that the Rods are actually the Dark Weapon of the Dark Lord and the key to her power, and monsters are doing everything to retrieve them. The Dragon Orb takes them back to the palace, where 'Rao' suddenly appears and asks for the Rods; Amaterasu promtly handing them over.
Upon returning the Orb to Otohime, the Orb presents a vision of Rao being chased down by a massive shadowy beast at Ankoku Temple, and not knowing if the revelation was past or present, Amaterasu and Issun returned there to save her. Later, when Himiko is found dead, 'Rao' tries to explain that a huge creature came and killed her, but then the duo realise that 'Rao' is actually the Dark Lord Ninetails in disguise; and that the Dragon Orb's revelation was revealing how the real Rao was murdered. Ninetails then mocks them for returning her source of power, the Fox Rods to her, enabling her to break the magical protection of Himiko's crystal ball and kill her, thus eliminating the only one who could locate Oni Island.
When Amaterasu battles Ninetails on the roof of Oni Castle, she uses Thunderstorm to split the spirits of the Fox Rods from their master, so they can be fought. When divided from Ninetails, the Tube Foxes take the appearence of multiple Rao with fox's faces, a form used by Ninetails previously. The Fox Rods are presumably destroyed following the defeat of all the Tube Foxes, reverting their master back into her weaker, original state.
Spoilers end here.
Like the Tube Foxes, the Fox Rods have their bases in mythological Kuda-gitsune.