Sayo Kadoya (門矢 小夜 Kadoya Sayo) is Tsukasa's younger sister. She is a pianist and is protected by Nobuhiko Tsukikage due to her possession of the Stone of the Earth, which is the source of Dai-Shocker's travel between the A.R. Worlds. This allows her to become High Priestess Bishium (大神官ビシュム Daishinkan Bishumu), whom Shadow Moon manipulated to hate Tsukasa and turn Yusuke into her puppet. After realizing that she has been used, she destroys the Stone of the Earth and later makes amends with Tsukasa before he leaves.