Kidou Minobe is the primary antagonist of the narrative and the acting chief of the Koga clan. His background is defined by physical infirmity and profound bitterness. Born with disabilities that prevented him from becoming a functional ninja, he was subjected to excruciating and ultimately futile experimental medical procedures during his childhood. These left him with permanent physical and emotional scars. The subsequent rise of his younger brother, Kishimaru Minobe, as a successful ninja fueled a consuming envy and resentment within Kidou, which eventually hardened into a deep-seated hatred for all ninjas and their traditions.

Personality-wise, Kidou is the embodiment of cruelty, manipulation, and a complete lack of empathy. He takes great joy in controlling others and eliminating anyone he deems a failure or a coward. His ultimate motivation is the eradication of all ninja clans. His ambition is to position himself as the last ninja, after which he plans to rule Japan with an army of robotic ninjas under his command. He is openly unrepentant, rejecting any notion of guilt and feeling no remorse for his actions.

Within the story, Kidou serves as the master strategist instigating the conflict between the Koga and Iga clans. He orchestrated the assassination of his own brother, Kishimaru, and then framed the rival Iga clan for the murder to justify a war of annihilation against them. He consolidates power within the Koga clan through fear and violence. When an elder named Housen Ban opposes the planned invasion of the Iga village, Kidou shoots him dead in the middle of a meeting to silence dissent. He also manipulates other clan members, such as Suzaku Ban, by exploiting their personal grudges to secure their loyalty. Beyond the ninja world, Kidou collaborates with corrupt officials, notably Genji Karajishi of the NSC, to fabricate evidence and eliminate political obstacles.

Kidou's key relationships are defined by exploitation rather than connection. Most notably, he fathers multiple children through concubines, only to murder the mothers after childbirth and implant control microchips in the children's brains. He views his offspring purely as tools for his schemes. For instance, his daughter Satomi Tsubaki is sent to assassinate the Iga heir, Ittoki Sakuraba, while another daughter, Kousetsu, is unknowingly embedded as an infiltrator within the Iga village. He exhibits no parental love, activating Kousetsu's microchip remotely in an attempt to force her to assassinate the Iga leader, Yumika Sakuraba.

In terms of development, Kidou remains resolutely static in his villainy until his death. He rejects a truce with the Iga clan that is offered during the final confrontation. He instead dons a mechanized ninja armor and attacks Ittoki and Kousetsu. After being defeated by Ittoki, who chooses to spare his life, Kidou attempts a final sneak attack. He is intercepted and killed by Tokisada Kaga, who exacts vengeance for the death of his sister, Yumika, and for Kidou's broader atrocities. His last words mock Ittoki's mercy and reaffirm his own unrepentant nature. His notable abilities are largely technological rather than physical; he is a proficient manipulator and strategist, and he commands a formidable force of mechanized Asura ninjas. In combat, he relies on a powerful mechanized suit of armor that enhances his strength and weaponry, compensating for his physical disabilities.