The Kamen Rider Club discovers that the Dai-Zangyack fleet is moving towards Earth, led by Captain Marvelous as their Great Emperor. With many revived Super Sentai villains under his command, Captain Marvelous plans to obtain the Great Power of the Kamen Riders which is said to be "Ultimate Treasure in the Universe". Meanwhile, Tsukasa Kadoya becomes the Great Leader of Dai-Shocker once again and recruits past enemies of the Kamen Riders to take down the Super Sentai teams.
The Game World launches an attack on the real world. In front of Kamen Rider Ex-Aid and the Uchu Sentai Kyuranger appears the "Arena of Death" where the destruction of the Earth will be decided. Trapped in this inescapable dimension, generations of Super Sentai and Kamen Riders must engage in a battle royale, an unprecedented battlefield of many puzzles connecting the real and game worlds. And then, "Those Heroes" revive... Everything is scaled up, all rules are broken! And when it seems like the real world will fall into a disaster, imagination brings forth unimaginable new heroes!
The Underground Empire Badan makes its move, intending to invert the world. Kouta and Mai are pulled through one of these inversions where the discover a boy named Shu, who also holds the power to invert the world. As the Riders fight to protect Shu, Fifteen appears again, seeking Shu. As Kouta flees, past Riders gather and fight one another, split between the Showa and Heisei era Riders. But, the truth of Badan is not as it seems…
A new evil organization known as Space Shocker, which are led by the magic-using Space Ikadevil and Space Spider Man, threatens the Earth by causing an unknown phenomenon. The Space Sheriffs Gavan type-G and Sharivan are sent to execute all magic-users on Earth in response to the threat and begins to attack Kamen Riders Wizard and Beast. The Space Crime Syndicate Madou, who were once defeated by the original Sharivan return, to cause even more havoc in the world. During this, Yoko finds a mysterious little robot called Psycholon, which Space Shocker and the Madou are after for unknown reasons.
The evil organization Shocker alters history by sending their newest creation, Kamen Rider 3, to defeat Kamen Riders 1 and 2 back in 1973. In the alternate present, Shocker is more powerful than ever, and most of the Kamen Riders are now either imprisoned or brainwashed to work for them. One such brainwashed Rider is Shinnosuke Tomari who thanks to his partner Kiriko Shijima, remembers the truth and joins forces with the remaining Kamen Riders who are still at large to make a stand against Shocker and put history back on its proper course.