Sayo Kadoya is the unwitting secondary antagonist of All Riders Vs. Dai-Shocker. She is Tsukasa's younger sister and is protected by Nobuhiko Tsukikage. She is the one who allows for Dai-Shocker's travel between the A.R. Worlds, due to her possession of the Stone of the Earth.
When she and Tsukasa were kids, Tsukasa would travel through dimensional worlds into other A.R. Worlds while Sayo stayed cooped up in her room. Later, after Tsukasa became the Great Leader of Dai-Shocker, he mysteriously disappeared due to losing his memories and left Sayo behind.
Tsukasa later returned and met Sayo and their butler, Nobuhiko Tsukikage again, and later resumed his role as leader of Dai-Shocker. However, Tsukikage then revealed himself to be Shadow Moon and usurped control of the organization, manipulating Sayo into hating Tsukasa and using the stone to become High Priestess Bishium. She eventually realized that she was being used and destroys the Stone of the Earth before making amends with Tsukasa.