|This article is about a/an set of locations in Kamen Rider Decade.|
The characters of Kamen Rider Decade exist amongst various different iterations of reality within the series referred to as an A.R. World (Another Rider's World). The New Worlds (新たな世界 Aratana Sekai) are the A.R. Worlds that are not based on a previous entry of the Kamen Rider Series from the Heisei period.
World of Negatives
- Main article: World of Negatives
The World of Negatives (ネガの世界 Nega no Sekai) is a parallel world created in the image of the one Natsumi and Tsukasa come from, but is actually home to monsters who assume human form and serve Dark Riders (ダークライダー Dāku Raidā) who hunt down any real humans that are still alive. The backdrop used to enter this world depicts the destruction of the first world caused by the monsters' conflict among themselves, the scene itself matching up with the mother and child running from the flames in the first episode, just before the event was frozen by Wataru Kurenai.
World of Diend
- Main article: World of Diend
The World of Diend (ディエンドの世界 Diendo no Sekai) is the world where Daiki comes from, similar to the World of Blade due to the presence of Undead known as Roaches (ローチ Rōchi). But as the world is dominated by them and their leader Fourteen, the human populace is mostly brainwashed into a state of euphoria and conditioned to see Kamen Riders as disruptors of the peace. The backdrop used to enter this world depicts a wanted poster with Diend's symbol on it in the foreground and a cityscape in the background. Within this A.R. World, Tsukasa assumes the role of a traveling salesman before being labeled a criminal.
World of Shinkenger
- Main article: World of Shinkenger
The World of Samurai Sentai Shinkenger (侍戦隊シンケンジャーの世界 Samurai Sentai Shinkenjā no Sekai) is the reality in which the Super Sentai Series, Samurai Sentai Shinkenger takes place. The backdrop used to enter this world resembles the ending credits sequence of Shinkenger, featuring two kuroko opening up a curtain to reveal artistic representations of the five main Origami. Because it is initially a world without Kamen Riders, the World of Shinkenger is not an A.R. World until Chinomanako obtains the Diendriver and transforms, becoming a distortion that threatens the world itself. The storyline takes place after Shinkenger Acts (episodes) 20 and during Act 21, with the episodes airing on July 12 and July 19, 2009. Within this world, Tsukasa finds himself as one of the kuroko of the Shiba Household, discarding the guise when the distortion begins.
World of Black RX
- Main article: World of Black RX
The World of Kamen Rider Black RX (仮面ライダーブラックRXの世界 Kamen Raidā Burakku Āru Ekkusu no Sekai) is the version of reality where Kamen Rider BLACK RX takes place. The backdrop used to arrive in this world features the Crisis Empire's battleship in the background. Within this A.R. World, Tsukasa originally wore a set of clothes that have him mistaken for Joe the Haze (霞のジョー Kasumi no Jō) by Kotaro and the Crisis Empire.
World of Black
- Main article: World of Black
The World of Kamen Rider Black (仮面ライダーブラックの世界 Kamen Raidā Burakku no Sekai) is the version of reality where Kamen Rider BLACK takes place, a parallel world to the World of Black RX. Apollo Geist arrives in this world prior to its RX counterpart, recruiting the cult Gorgom as a result.
World of X-Rider
- Main article: World of X-Rider
The World of Kamen Rider X is a version of reality where Kamen Rider X takes place. Apollo Geist originally came from this world, where, differently from his original counterpart, he obtained a Perfecter after his resurrection, avoiding an early death against X-Rider.
World of Amazon
- Main article: World of Amazon
The World of Kamen Rider Amazon (仮面ライダーアマゾンの世界 Kamen Raidā Amazon no Sekai) is the version of reality where Kamen Rider Amazon takes place. By the time Decade arrives, he finds the world is under Dai-Shocker's control as they eliminate any resistance. As a result, the people do not trust each other, as they cannot tell who is and who is not aligned with Dai-Shocker. The backdrop used to arrive in this world depicts the Amazon Rainforest with Amazon in the middle of it. Within this A.R. World, Tsukasa wears the attire of a baseball player.
World of the Rider War
- Main article: World of the Rider War
The World of the Rider War (ライダー大戦の世界 Raidā Taisen no Sekai) is the iteration of reality where the Rider War takes place and is the reality that is the confluence of the Nine Worlds. The backdrop used to enter this world depicts all nine of the Heisei Riders, the DenLiner, Dragredder, Castle Doran, and Ryokuōzaru rushing at Decade, mirroring the very opening scene of the series. Going into the World of the Rider War, the only "worlds" remaining are of Blade's, Kiva's and Hibiki's.
World of Decade
- Main article: World of Decade
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. 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.
World of the Rider War (Movie War 2010)
- Main article: World of the Rider War
In Kamen Rider Decade: The Last Story, Tsukasa, Kaito, and the Hikari Studio crew continue in the World of the Rider War, now further combined and transformed into the final battlefield of the Kamen Riders and home to the evil Super Shocker organization. The backdrop for this world now depicts the destruction of the Nine Worlds.