Synopsis

The story revolves around the nine previous universes of the Heisei Kamen Riders merging into one, something that would destroy all the worlds. To prevent this, Tsukasa Kadoya transforms into Kamen Rider Decade to protect his own dimension by defeating the Kamen Riders of the other dimensions.

Rider War

The Rider Army (ライダー軍, Raidā Gun) first revealed in Natsumi Hikari's dream, composed of many Kamen Riders, all of whom where 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 t o Natsumi, it will be the Rider War that awakens Decade as the demon destined to destroy all the worlds.