The Camp Cretaceous gang comes together to unravel a mystery when they discover a global conspiracy that brings danger to dinosaurs — and to themselves.

"Mirror World" exists symmetrically beyond an invisible mirror in space, and an exact copy of our human world, where only monsters can dwell. Evil monsters frequently cross the mirror and attack our world. Only Kamen Riders who make a contract with a specific monster and obtain special power from it, can enter "Mirror World" and fight against evil monsters with the help of an "Advent Card." Shinji Kido, a journalist, contracts with a dragon and becomes Kamen Rider Ryuki. He fights a fierce battle with evil monsters. Many Kamen Riders appear one after another and fight to satisfy their own aims. However, only one Kamen Rider can outlive others. Thus, it is their fate to keep fighting to the last man.

Following the fall of Gorgom, Kotaro Minami tries to live a normal life with the Sahara family. However, this brief moment of peace is soon shattered by the arrival of the Crisis Empire, an evil alien menace that aims to eradicate humanity and claim dominion over Earth. After refusing to aid them in their nefarious goals, Kotaro is thrown hurtling back towards the planet with his transformation belt shattered. However, when he awakens, Kotaro discovers that the sun’s rays have blessed him with new power, the power of Kamen Rider Black RX!