Ten thousand years ago, a massive battle known as the Battle Royal was fought by fifty-two demons known as the Undead, each reprisenting a species fighting for dominance over all others. The winner was the human undead known as category two of hearts giving domination of the Earth to humanity, in the present day, archeolegists discover the sealed Undead, and accidentally set them free. Thus a new Battle Royal begins. Having developed the Rider System, based on the Joker's ability to copy sealed Undead, the orginazation BOARD (Board of Archaelogical Rider Department) equips two young men, who become Kamen Riders: Jared McCormick and James Anderson fight together as Kamen Rider Ace Warrior and Diamond Paladin to protect humans from Undead and seal them. Also fighting the undead is the mysterious Heart Archer, a Kamen Rider whose purpose is unknown. In addition, a young man struggles to free himself from the control of the sealed undead powering it's Undead-made Rider System, fighting as Kamen Rider Clover Lancer.
