After Natsumi Hikari has a nightmare of every Kamen Rider being defeated by a figure called Decade, she helps her grandfather Eijiro deal with unsatisfied customers. The photographer, Tsukasa Kadoya, seems to be at fault, but he simply tells Natsumi the photos are bad because he does not belong in this world. After the argument, various holes in reality open, allowing the Orphnoch, Undead, Makamou, Worms, Imagin, and Fangires to start terrorizing their world. In the bedlam, she finds a corroded belt and book, recalling it as Decade's from her dream. She gives Tsukasa the belt and book, allowing him to transform into Kamen Rider Decade by using a card from the book and inserting it into the belt.
