Kamen Rider Decade was the title of the first of the 2009 editions of the long-running Kamen Rider Series of tokusatsu dramas. Decade, as its title suggests, is the tenth of the Heisei Rider Series, having begun with Kamen Rider Kuuga in 2000. It began broadcast the week following the finale of Kamen Rider Kiva. The series ties in with the arcade game Kamen Rider Battle: Ganbaride, with Kamen Riders Decade and Diend using cards resembling those used in the game to transform and access various weapons. The catchphrase for the series is “Destroy everything, connect everything.”
The story revolves around the nine parallel universes of the previous Heisei Kamen Riders merging into one, something that would destroy all the worlds. To prevent this, Tsukasa Kadoya transforms into Kamen Rider Decade and is told that to save his own world he must travel with Natsumi and her grandfather to the other Kamen Riders’ Worlds called A.R. Worlds (Another Rider’s World or Alternate Reality World) and defeat the other Kamen Riders. Along the way, confronting the mysterious Narutaki and the thief Daiki Kaito, they are joined by Yusuke Onodera of the World of Kuuga and Kivala of the World of Kiva.
To fit with the printing motif of the series, the main Kamen Riders of the series follow the CMYK color model: Decade is magenta, Diend is cyan, and Kuuga (Rising Ultimate Form) is black and yellow. In the Cho-Den-O Trilogy film Episode Yellow: Treasure de End Pirates, Diend is the primary character, emphasizing the yellow accents on his Diendriver and the enhanced Kamen Ride Diend card.
The Rider War, first revealed in Natsumi Hikari’s dream, is a predestined event composed of many Kamen Riders called the Rider Army, all of whom were seemingly defeated by Kamen Rider Decade. However, Kamen Rider Kuuga survived the initial battle, assuming Ultimate Form to confront Decade once again with the two seemingly destroying each other in the ensuing battle. As Narutaki explains to Natsumi, the dream is a predestined event in which Decade will destroy all the worlds.