The Hikari Studio arrives in a new A.R. World where, after seeing that Tsukasa's photos of this world are coming out perfectly, Natsumi realizes they may be in Tsukasa's home world. Tsukasa realizes he remembers the mansion depicted on the backdrop that took them here. Finding the manor, Tsukasa opens the door as he Natsumi and Yuusuke meet a girl named Sayo,who identifies Tsukasa as her older brother. As Sayo learns that Tsukasa lost his memories, revealing how he left her a year ago, her caretaker Nobuhiko Tsukikage arrives and confronts him about leaving his sister alone for so long. But when the Nine Worlds fusion starts to influence the World of Decade, Tsukikage reveals that Tsukasa's journey has now enabled a solution to the crisis by determining the strongest Kamen Rider in existence: The Rider Battle.