The World of Decade (ディケイドの世界 Dikeido no Sekai) is the version of reality that is the true home of Tsukasa Kadoya (Kamen Rider Decade). It is the primary setting of Kamen Rider Decade: All Riders vs. Dai-Shocker. The backdrop used to enter this world depicts an old mansion that is the home of the Kadoya family. This A.R. World is neither one of the Nine Worlds nor the New Worlds. This is the world where Daiki got his first treasure, the Diendriver.