|Name: Zaomaru Zaitsuhara|
|Designation: Kamen Rider Zanki|
|Weapons: OngekiShingen Retsuzan, Ongekishin Zantetsu|
|Gear: Onka, Raijin|
|Zaoumaru Zaitsuhara is the oldest of the four main Oni in the series. Being the seasoned vet, even Hibiki saw him as a superior, even though Hibiki had once trained Zanki in the use of Taiko. Zanki was first mentioned in episode five, when after defeating the Douji of a Bakegani, him and his disciple Todoroki were forced to retreat after being attacked suddenly by the Bakegani itself. In this form, Zanki is a bronze demon that looks like Todoroki. To become this form, Zanki simply needs to pluck his brace strings, the vibrations from the strings cause his body to be hit by massive lightning bolts, changing him into his Oni form. Zanki also gains a second "oni face" which is a crest that forms on his forehead. Unlike most Kamen Riders, Zanki does not wear a suit, rather his demon form is his true form. During their first on screen battle during episode fourteen, Zanki literally falls to his knees in pain as he battles a Douji/Hime with Todoroki. At his age and due to his wounds, Zanki is no longer able to fully engage Makamou in battle. Later on Zanki says that his time to retire has come and that Todoroki is to take the mantle of Zanki. Todoroki resists and says that he wants to make his own name, thus allowing Zanki to keep his Oni name.
At first he sees Todoroki's style of cleansing the battlefield to not be traditional and as unneeded but eventually comes to understand that this is his student's way of fighting Makamou and that all Oni have their own way of doing so. Later on, Todoroki begins to fall to fatigue in battle due to not having a supporter. Both Hibiki and Ibuki have Kasumi and Akira to help them with disc animal operation yet Todoroki is alone on his missions. Todoroki's fatigue begins to show in his battles and he becomes sloppy with the way he battles Makamou. Eventually Zanki decides that he will take on the role of a supporter for Todoroki and help guide him as Todoroki feels that he still needs the help of Zanki to be a great Oni warrior on his own. Zanki's mentor, Shuki, returns and steals Todoroki's Henshin Onsa OnKaku and once again transforms into her Oni form. Zanki has a troubled past with Shuki, she would go to great lengths to destroy all Makamou as they were the cause of her family's death. This was the only reason Shuki became an Oni and meant that she was not a pure Oni. As a young Oni, Zanki was caught in the mouth of the Notsugo that murder her family, Shuki aimed her attack straight into Zanki's chest, hoping to kill the Makamou. Both Zanki and the Makamou survived as Shuki missed at the last second, but the attack was the reason for Zanki's declining health over the course of the series.
In the final battle of Notsugo, Shuki was caught in its mouth much like Zanki many years ago, despite Shuki's orders to attack the Makamou with her in its mouth, Zanki would not attack his former teacher despite his contempt for her. Shuki then committed suicide as she aimed her weapon at herself, wounding the monster for an enraged Zanki to finish off. Zanki would go on to bury his teacher in a garden of flowers as her final wish for no one to see her true face. Zanki once again became an Oni, despite being told by his doctor that going into any more battles would result in Zanki shortening his life every time he transforms. During a battle where Todoroki was left immobile, Zanki had to step in to fill his spot. The night before his death, Zanki used a forbidden spell Shuki taught him on his soul that would not let it leave the mortal realm until his mission was fulfilled. However this same spell would result in the decay of his human soul should he remain among the living for too long.
During a battle with a group of Makamou, Zanki was killed in an ambush by a pack of Bakeneko taking advantage while he left himself open for attack. Ibuki found his naked body and realized that Zanki was dead when he felt no pulse. Despite this, Zanki appeared in Todoroki's hospital room that night to comfort his student. Over the course of the next few days, Zanki helped Todoroki regain the ability to walk and finally transform again. In his last battle, Zanki was joined by Todoroki as the two battle a Kaengumo and pack of Bakeneko. At the end of this battle, Zanki and Todoroki cleansed the battlefield in Todoroki's style. As Todoroki bowed to his master, Zanki disappeared, his mission of seeing his greatest student become independent fulfilled, Zanki's soul could now rest in peace.