In the fall of 2018, a time machine appears before Sougo Tokiwa, a high schooler that has always dreamed of becoming a king. Then, Tsukuyomi appears from the time machine, telling the hero “I come from the year 2068, a world without hope where the Oma Zi-O, the king of time reigns supreme.” She has come from the future in a desperate effort to change her own time. She then gives the hero an ominous warning “You will become Kamen Rider Zi-O, King of Time, the overlord destined to rule the world.” Can this really be the hero’s fate? This is the story of a Kamen Rider who would be king, who will fight to save the past, present, and future, encountering the various Heisei Kamen Riders throughout space-time.
Each episode in Kamen Rider Zi-O ends with the year (except the episode's event happend in the present and is related to Zi-O himself) that relates to the time of the original Legend Rider. Like the first two Rider series, each episode still use the English language in most of their parts of the episode's title.
This is the first series since Fourze to have the titular rider only appear at the predecessor's summer film while OOO is the first have the transformation device appearing at the predecessor's series only.
On Zi-O's official Twitter page, there is an error on the banner that shows Ryuki wearing the Decadriver. This error was fixed as the banner have several Riders covering Ryuki's lower body. However, the image of Ryuki wearing the Decadriver remains on the banner.
This is the first series since Ghost to feature secondary writers plotting the episodes.