Genzo Kuruma serves as the primary antagonist. He is a scientist and leader of a sect dedicated to awakening a god-like entity, possessing green hair, a breathtaking beard, epic eyebrows, and notable facial hair. Genzo is driven to obtain a specific blood type essential for the god's resurrection, found only in his son Shinichi Kuruma and a young girl named Ayaka Sanders. He relentlessly pursues them for their blood, disregarding the consequences for humanity. His actions directly cause widespread destruction, including near-total devastation of civilization through catastrophic events linked to the entity's partial awakening.

His background includes conducting unethical experiments on his own family. He subjected his son Shinichi to genetic modifications that granted the ability to summon beasts and absorb their powers. These experiments extended to Shinichi's mother, Genzo's wife, ultimately causing her death, fueling Shinichi's desire for vengeance. Genzo leads a group called the "13 Doctors" or "Apostles," who assist in creating genetically altered soldiers known as "New Humans" or "Newmen," capable of transforming into monsters. His operations employ kidnapping and violence to achieve the necessary blood extraction.

His scientific work involves cloning the god entity, resulting in multiple clones with differing dispositions. One clone, Noah, exhibits a merciless attitude toward perceived sinners and possesses a third eye. Genzo creates these clones using blood isolated from Shinichi, originally derived from Maria Tengai. His disregard for ethical boundaries extends to sacrificing cities and civilians to eliminate threats or advance objectives, such as bombing a train and a small city to target Shinichi. Genzo embodies ruthless ambition, leveraging his scientific expertise and leadership of the Apostles to pursue divine awakening at any cost, positioning himself as the pivotal force behind the apocalyptic conflict.