A.R. World

The characters of Kamen Rider Decade exist amongst various iterations of reality within the series referred to as an A.R. World (Another Rider's/Alternate Reality World). The Nine Worlds (9つの世界) are the A.R. Worlds that are based on the previous entries of the Kamen Rider Series that have aired during the Heisei period of Japanese history. Each differs in some way from the series on which it was based. The New Worlds (新たな世界) are the A.R. Worlds that are not based on a previous entry of the Kamen Rider Series from the Heisei period.

Nine Worlds

 * World of Kuuga
 * World of Kiva
 * World of Ryuki
 * World of Blade
 * World of Faiz
 * World of Agito
 * World of Den-O
 * World of Kabuto
 * World of Hibiki

New Worlds

 * World of Negatives
 * World of Diend
 * World of Shinkenger
 * World of Black RX
 * World of Black
 * World of Amazon
 * World of the Rider War
 * World of Decade