Seven years prior to the series, a meteorite struck the Shibuya district in Tokyo. An alien lifeform, known as the Worms, emerged from the meteorite and became a threat to humanity. Souji Tendou has been trained for seven years while waiting for the Kabuto Zecter so that he may properly take up the mantle of Kamen Rider Kabuto. Making many enemies while at the same time meeting other Riders with mysterious origins, Tendou attempts to accomplish his goal at all costs: to destroy all Worms that threaten humanity. He meets ZECT operative Arata Kagami, who later becomes Kamen Rider Gatack. The two soon work together to save humanity from the alien Worms—but not before uncovering the conspiracies within the ZECT organization and the "Natives" species.

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