Nine universes of the previous Kamen Riders merging into one that would destroy all the worlds. Tsukasa Kadoya transforms into Kamen Rider Decade and travels to all of the Another Rider's worlds and eliminate the anomalies in those worlds.
The Game World launches an attack on the Real World. In front of Kamen Rider Ex-Aid (2016) and Uchu Sentai Kyuranger (2017) appears the "Arena of Death" where the destruction of the Earth will be decided.
Eiji and Ankh team up with Kotarou and Momotaros as they travel back in time to stop the Imagin. But Ankh's desire to obtain Core Medals while in the past sets off a chain of events that alters the history of the Riders and the world.