This article is about a/an alternate reality/A.R. World (another rider's world) in Kamen Rider Decade.
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, Kamen Rider Decade.