Thousand-Year Evil

The Thousand-Year Evil (Sennen Jaki)  is a malignant mass of energy from the original Org invasion 1,000 years ago. Using a wolf mask known as the Dark Mask, Shirogane harnessed its power to combine his three Power Animals into GaoHunter and thus be able to kill Ultimate Org Hyakkimaru. However, even though he managed to finish off the Org, the evil spirt took full control of Shirogane's body which ended up transforming him into the Duke Org Rouki, while transforming GaoHunter into GaoHunter Evil, and its components into Demon Beasts in the process. Unable to control its power, Shirogane had his allies seal him in a stone coffin to avoid harming anyone.

Centuries later, Rouki is released by the Highness Duke Org Ura to fight against the Gaorangers, remembering only his millenium imprisonment by the original Gao heroes. Over time, Rouki began to remember who he was, butUra implants a special grasshopper in him to modify his memory and turn him into his obedient servant. Rouki is then defeated by the Gaorangers, who manage to defeat GaoHunter Evil to break the curse, freeing both Shirogane and his Power Animals from the malign power in the process. Later, the Thousand-Year Evil used the Dusk Mask to return as Rouki, intent on killing Shirogane for using his power. In the end, Rouki is finally defeated by the combined efforts of GaoSilver and Gaorangers, with him finally killed by GaoHunter Justice. Although the Dusk Mask is destroye, the Thousand-Year Evil survived. Ura would then use it to create`new powerful Orgs to fight the Gaorangers, while giving the Duchess Org TsueTsue and the Duke Org Yabaiba residual energy to transform them into their Armored Forms and increase their powers.

With each Org created with the evil energy that was defeated, the Thousand-Year Evil's grudge matured, causing it to increase in power. Eventually, after the Gaorangers defeated Tombstone Org, they used the newly formed Gaokung Crosshorn to imprison the spirit so it could not be used to make anymore Orgs. Despite being sealed, however, the spirit was still out there.

Ura then captured Shirogane, intent on making him reabsorb the evil power to turn into Rouki. Using Shirogane's weapon, Ura broke the seal on the Thousand-Year Evil and allowing it to reenter Shirogane's body. While it at first looks like it was overwhelmed him, Shirogane managed to reject the spirit, finally severing his millenium bind to it. However, this was actually what Ura wanted, enabling him to use his mirror to absorb the Thousand-Year Evil and evolve into a more powerful form, which he reveals was his plan from the very beginning of his reign. With the power of the Thousand-Year Evil inside him, Ura massacred the Gaoranger, leaving Kakeru and Shirogane as sole survivors. While trying to fight the strengthened Ura on their own, the other Gaorangers provide GaoRed the Falcon Summoner and GaoFalcon from the other world, while GaoGod revives them to help out with GaoIcarus. After a battle, Ura is purged of the Thousand-Year Evil after being wounded GaoIcarus, returning him to his original form. Ura is wounded by GaoSilver and finally killed by the Hyakuujuuken wielded by Gaorangers, destroying the Thousand-Year Evil forever, while Tsuetsue and Yabaiba return to their original form as a result.