Onigashima (「鬼ヶ島」?) is an island visited by the Japanese folk tale character Momotarō. Momotarō left his parents to fight a band of marauding oni on the distant island of Onigashima. En route, Momotarō met and befriended a talking dog, monkey, and pheasant, who agreed to help him in his quest. At the island, Momotarō and his animal friends penetrated the demons' fort and beat the band of demons into surrendering. Momotarō and his new friends returned home with the demons' plundered treasure and the demon chief as a captive. Momotarō and his family lived comfortably from then on.
The island has been linked to the real world island of Megijima (「女木島」?). Megijima is an island located in the Inland Sea of Japan, north of the city of Takamatsu, and is part of Kagawa Prefecture. The caves at the top of Washigamine Summit, as the home of the ogres from that story, are a popular tourist spot. There is an observation platform at the peak of Washigamine Summit where tourists can get a 360 degree view of the Seto Inland Sea.
Oni Island is based off of Onigashima, serving as the home of Ninetails. Amaterasu and Issun travel to the island to exterminate the demon lord Ninetails in order to bring peace to the western half of Nippon.