Millions of years ago, species of animals fought on the Earth for dominance. These species were called the Undead, and humanity (somehow) won the great battle. In the present, someone carelessly released all the Undead, so it's up to 4 Kamen Riders to stop them. But by catching up to and sealing the Undead, things seem to get bleak. In a last ditch effort, the main character, Kazuma Kenzaki, must fight the greatest adversary, Joker Undead