Otowa no Jōko, a name also rendered as Otowa no Kido, is a central antagonist in the Watari story. He is introduced as a middle-ranking ninja of the Momochi faction of Iga and the faction's head retainer, serving the lord Momochi Sandayū. His true nature, however, is far more complex: he is simultaneously Tateoka no Michinobu, the head retainer of the rival Fujibayashi faction, and it is revealed that the supposed rivalry between the two factions is an elaborate deception engineered by this one man. By maintaining two separate identities, Jōko manipulates both the Momochi and Fujibayashi lords from behind the scenes and rules all of Iga as its secret master. He deliberately split the province's ninja into feuding camps so that their discontent would be directed at one another rather than at the ruling class he controls.

Jōko's background is closely tied to the oppressive system known as the death oath, the mysterious order that governs the lives of lower-ranking ninja and decides who is to be killed. He is the hidden architect of this system, and his role as the shadow ruler of Iga comes to light through the investigations of the wandering young ninja Watari and his elder companion Shikanme. When the truth behind the death oath is exposed and the existing ruling order collapses, Jōko attempts to justify himself by insisting that he only obeyed the commands of a true master, but the resistance leader Ishigawa no Obitto dismisses his plea without sympathy. The resistance group known as the Akame faction, formed by lower-ranking ninja, takes control of Iga and has Jōko imprisoned and chained.

Jōko does not remain defeated for long. He is eventually freed by a mysterious armored warrior called the Zero Ninja and, with that figure as his backing, is restored to power over Iga. The Zero Ninja appears to be an invincible enemy who returns no matter how many times he is defeated, but his secret is that he is not a single warrior at all: Jōko has controlled a succession of ninja through hypnotism, using them as disposable instruments to terrorize his opponents. This reveals the core of Jōko's method, for he prefers to rule indirectly, through manipulation, illusion, and expendable agents, rather than through open force.

A calculating, secretive, and ruthless figure, Jōko is driven above all by the desire to preserve his grip on Iga. He shows little regard for the lives of the ninja beneath him, and he is prepared to betray even his own instruments when it suits him. In his alternate identity as Tateoka no Michinobu, he is a capable fighter who uses a bladed weapon called the chi-biki, and when his identity is exposed he demonstrates formidable skill, cutting down the new Akame members who confront him with a technique known as the vacuum slash. His most notable abilities, however, lie beyond physical combat: mastery of disguise, the maintenance of two simultaneous identities, hypnotic control over others, and the strategic cunning to set entire communities against one another for his own benefit.

Jōko's arc carries him from hidden mastermind to exposed conspirator, then to restored tyrant and finally to desperate traitor. After Watari and his allies expose the Zero Ninja's true nature and corner Jōko, he signals the forces of the warlord Oda Nobunaga, with whom he has secretly been in league, to launch an invasion of Iga, effectively selling out the province he once ruled. He dies amid this final catastrophe. Throughout the story, Jōko stands as the principal antagonist to Watari, who embodies the ideal of a ninja bound to no master, and his most significant relationships are those with the lords he deceives, the resistance fighters who overthrow him, the hypnotized Zero Ninja he commands, and the outside warlord he ultimately turns to.