It is revealed that Tsukasa was the Great Leader of Dai-Shocker, an evil organization that is attempting to take over all dimensions. He commissioned the creation of the Decadriver in order to prevent the collapse of the A.R. Worlds and allow Dai-Shocker to conquer them. Tsukasa somehow suffers from amnesia and ends up in Natsumi Hikari's home dimension, where he gets the Decadriver and becomes Kamen Rider Decade. Finally, after fighting Dai-Shocker through the alternate worlds, he and Diend kill the last of the Dai-Shocker's active Leaders, Super Apollo Geist. However, it is eventually revealed that his true mission was to destroy the A.R. World Riders and their worlds, a role he undertakes as the Rider War commences, becoming Kamen Rider Decade Fury Form.
While he destroys all the other Kamen Riders except for Diend, Natsumi uses Kivara, to transform into Kamen Rider Kivara. Decade then willingly allows Kivara to impale him through the Decadriver. As she does this, he gives her the cards left behind when he killed the other Riders. His death is the catalyst for the restoration of all the A.R. Worlds and everyone who died in the Rider War, even those Decade didn't kill personally. Afterwards, the memories of his friends are used to revive him and he leads the other Kamen Riders in the final battle with the newly formed Super Shocker and the revived Neo Organism. After a long, fierce battle, he teams up with Kamen Rider Double to destroy the Super Crisis Fortress and use the Triple Extreme Kick to destroy the Neo Organism in the form of Ultimate D. Afterwards, he and his friends return to the Hikari Studio to continue in their journey across the A.R. Worlds.