Producer Shirakura stated that like Decade, Zi-O was the culmination of the entire Heisei-era, which would end when Prince Naruhito ascended to the Japanese throne in 2019. Viewership ratings from Build were at a new low, and Shirakura noticed that those ratings were 40% higher during Decade. Shirakura was also extremely hesitant to bring back former actors as well as deal with the tricky concepts of time travel like Den-O, but his associate producers convinced him to tackle them as Shirakura was willing to give it a try.
Both Gaim and Ghost had began the idea of having multiple Riders use the same transformation belt, similar to how Super Sentai Rangers transform using the same device but in a more controlled setting. Shirakura had liked the idea, and allowed both Geiz and Tsukuyomi to use a Ziku-Driver like Sougo to transform. During the original designing stages for Zi-O's suit, Shirakura was interested in the motif of time itself he felt it symbolized the Heisei-era, so "Rider" in katakana was added to Zi-O's mask for his default form. To differentiate Zi-O's means of transportation and time travel, the Time Mazine was introduced as opposed to a train and other supernatural means.
"Oma's Day! The judgment day marking the end of the Kamen Rider era. Is it the end of history or just the beginning? Choose our future!"
―Opening narration by Rikiya Koyama (episode 17-29)[src]
"The Heisei Kamen Riders have passed through this era. Inheriting all the powers, a new legend is beginning. Rejoice at the birth of the true king!"
―Opening narration by Rikiya Koyama (episode 30-40)[src]
"The Heisei Kamen Riders have passed through this era. With their powers now gathered, the curtain rises upon the final battle. Open the way to the future of the true king!"
―Opening narration by Rikiya Koyama (episode 41-48)[src]
Sougo Tokiwa, a high school student born in the year 2000, has always dreamed of becoming a king when he encounters a mysterious girl named Tsukuyomi, who hails from the future in a desperate effort to alter her dire future. She presents Sougo with an ominous warning "You will become the king of all time, Kamen Rider Zi-O, a demonic king destined to rule the world.”. Sougo takes up the mantle as Kamen Rider Zi-O to stop the Time Jackers from destroying the very fabric of space-time while protecting the legacy of the Heisei Kamen Riders that came before him. During his journey alongside Geiz Myokoin, a Kamen Rider from Tsukuyomi's future, and the mysterious prophet Woz who reminds Sougo of his demonic destiny, they will meet their esteemed predecessors who they must gain their trust and powers from in order to create a new future for the Kamen Riders and mankind itself. 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.
Episode 01-16 - Rider Time, the Demon King of Future (「ライダータイム、未来の魔王」編,Raidā Taimu, Mirai no Maō Hen), this arc introduces most of the main characters and the plot.
Episode 17-30 - Trinity Time, Servant and Demon King and Saviour (「トリニティタイム、従者と魔王と救世主」編,Toriniti Taimu, Jūsha to Maō to Kyūseishu Hen), this arc features White Woz who seeks to create GeizRevive, the 3 riders of the future, and the preparation of Oma's Day. It also shows Sougo’s past and how his dreams of becoming king came to be.
Episode 31-43 - Grand Time, the New Future (「グランドタイム、新たなる未来」編,Gurando Taimu, Aratanaru Mirai Hen), this arc deals with Tsukuyomi’s past as she regains her memories.
Episode 44-49 - End Time, the Destruction and Reborn of the World (「終焉の時、世界の破壊と再生」編,Shūen no Toki, Sekai no Hakai to Saisei), this deals with Swartz’s real plan to become king and Sougo becoming Ohma Zi-O.
Each episode title is written in either katakana or hiragana, and includes the year relevant to that particular episode, which is often the premiere year of the original Legend Rider in the case of tribute episodes. Starting with episode 30, this format is reversed, starting with the year first, then the title. Similar to the previous two Rider series, many episodes still use the English language in most of their parts of the episode’s title, though there are exceptions.
As the show pays tribute to the Heisei period Kamen Riders, each episode title consists of a short phrase related to a particular Heisei Rider series and a year relevant to it.
This season's concept of traveling across time through the previous installments is akin to an idea during the early development stages of Kamen Rider Decade, one of which would've been a "Kamen Rider Den-O 2", using the season's setting go travel across time around each rider's era.
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.
This is the first series sinceKamen Rider Gaim to not have a Blu-Ray miniseries.
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.
Incidentally, Decade would appear in the series as well as changing into Ryuki. However, he does not use the original Decadriver and instead uses the Neo Decaderiver.
This is the first series since:
Ghost to feature secondary writers plotting the episodes.
Den-O to not have spring film in production during the series run.
The actors of the three Future Riders' are Super Sentai alumni.
Interestingly, they all starred in the 2010s Super Sentai series.
Although the first two played Sentai Rangers, the third played a Sentai Villain.
The fourth Future Rider's (voice) actor also voiced Sentai Monsters of the week.
Not counting Rider Troops, this series has the highest number of unnamed identity Riders, being (currently) 38 people.
Currently, Kamen Rider Zi-O has the highest number of returning Legend Riders, being 65 at present (including stand-in and suit-only appearances).
When including those Legend Riders who did not appear transformed and so are counted as returning allies, this number is further increased to 69.
Including the Legacy Riders and Another World Legend Riders further increases the count to 87.
Zi-O also has the highest number of returning cast from the previous series, with 52 actors, 8 actresses and 8 voice actors (including some who returned but portrayed/voiced new character).
Minority unique of Zi-O for returning characters are:
Rina Akiyama returned to portray as Mana Kazaya from Kamen Rider Agito.
Yuichi Nakamura portrays two characters from two different series. So far, there is no Kamen Rider series to have one actor to portray two different characters from different series (not counting Kohtaro Minami for being a character with two series)