Oma Zi-O's Army are a collection of forces who serve the Demon King Oma Zi-O and an antagonist faction in Kamen Rider Zi-O.
After unlocking the powers of the past 19 Heisei Riders, Sougo Tokiwa became Oma Zi-O and began his conquest of the world. Using the Dai Mazines, Oma Zi-O reduced the Earth to ruins and wiped out half of all life. A Resistance soon arose to oppose Oma Zi-O and sent a spy to infiltrate Oma Zi-O's forces. However, the spy, Resistance Captain Woz, secretly defected from the Resistance and supplied them with faulty information in order to lure them to their demise against Oma Zi-O.
After Geiz Myokoin and Tsukuyomi traveled back in time to 2018 to change the past by stopping Sougo from becoming Oma Zi-O, Oma Zi-O's robotic servant Kasshin was sent back in time to eliminate Geiz. However, Sougo deactivated the robot by smashing his Ziku-Driver and altering the timeline so he wouldn't become Oma Zi-O. Kasshin was later reprogrammed by the Time Jackers to go eliminate Sougo, forcing Sougo to become Zi-O again.