Thirteen card decks were created for thirteen kamen riders. They make contact with monsters from the mysterious mirror world a Parrael world opposite to the real world where only riders can exist. The Riders draw on their monsters strength in exchange for feeding them life force of the creatures they destroy. The creator of the advent cards has only one rule: that there can only be one kamen rider. The others must be killed, and the sole victor will be granted a single wish, which leads to a conflict called the rider war.
