Jōji Kirishima is the primary antagonist of the Robot Keiji series, functioning as the leader of the criminal organization known as BAD. He is the younger brother of Dr. Saori Kirishima, the scientist who created the robot detective K. His background is marked by tragedy: after his father, Dr. Kirishima, was killed by a villain, Jōji became consumed by a deep hatred of humanity and a burning desire for revenge. This trauma directly motivated him to establish BAD, a syndicate that rents out specialized criminal robots to individuals who wish to commit crimes beyond the ability of humans. The illicit profits from these rentals are used to fund the organization's operations, which later escalate into a larger scheme for world conquest.

Jōji's personality is defined by a cold, calculating ruthlessness and a profound misanthropy. He views humans with contempt and sees his criminal enterprise as both a business and a means of striking back at the society he blames for his father's death. Despite his cruelty, he operates with a certain perverse professionalism, honoring contracts with clients who pay and punishing betrayal with lethal finality. His motivations are twofold: personal vengeance against humanity as a whole, and a pragmatic drive to accumulate power and resources through organized crime.

In the story, Jōji serves as the shadowy mastermind behind the robot crimes that the hero K and the police must investigate and stop. He directs BAD's operations from the shadows, deploying a wide array of specialized robots such as Kaminariman, Ganrikiman, and Gatling Man to commit murders, thefts, and acts of terrorism. His role is that of the ultimate antagonist whose machinations drive the central conflict, culminating in a final confrontation that reveals his true identity and the full scope of his ambitions.

Jōji's key relationships are defined by family and opposition. His relationship with his sister Saori is one of bitter enmity, as Saori created K specifically to combat the threat of his criminal robots and to stop his destructive path. His connection to K is one of direct opposition, with the robot detective standing as the primary obstacle to his plans. He also commands a number of lieutenants and cyborg soldiers within BAD, though these relationships are transactional and based on fear rather than loyalty.

Development-wise, Jōji undergoes little change throughout the narrative. He remains steadfastly committed to his revenge and his criminal goals until his final defeat. His backstory, revealed gradually, provides context for his actions but does not lead to redemption or second thoughts. He is a figure driven by grief and hatred who chooses to embrace villainy rather than seek any other path.

Notable abilities include his strategic and organizational talent in running a criminal empire, his access to advanced robotics and technology, and his ability to command a network of deadly robotic enforcers. He also possesses significant resources and a hidden base of operations, including the gigantic fortress known as Mother. He is not portrayed as a physical combatant himself, relying instead on his robots and soldiers to do battle. His true power lies in his intellect, his resources, and his willingness to use any means necessary to achieve his ends.