In the fall of 2018, a time machine appears before a hero born in the year 2000. The hero has always dreamed of becoming a king. A mysterious girl appears from the time machine, telling the hero “I come from the year 2068, a world without hope where the king of demons reigns supreme.” The girl has come from the future in a desperate effort to change her own time. The girl then gives the hero an ominous warning “You will become Kamen Rider Zi-O, King of Time, the demon 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.
Sougo Tokiwa seems like an ordinary high school student, but one thing he has different is that he has dreams of becoming a king! One day, a mysterious young man appeared before him with a prophecy. "Congratulations! Today is a special day for you..." As Sougo is told these words, a giant red robot suddenly appears before him! This robot was a time machine, and Sougo was thrust across various timelines! In the year 2000, the battle of the Heisei Rider's fate, and Sougo's fate in his own birth year, is about to begin...!
The man who hails from the future, Geiz, attacks Sougo! Tsukuyomi, a girl who also hails from the future, came to help out Sougo, but Sougo has absolutely no idea what's going on! A mysterious prophet named Woz is also starting to appear frequently before Sougo. The creature, Another Build also attacks. What could be the key to defeating this "Kamen Rider Build"? Sougo makes his way towards the Nascita Cafe to meet with Kiryu Sento...
A strange collaboration between Geiz and Tsukuyomi happens with Sougo in the year of Build, 2017. They both decide to go to Sougo's school to keep a closer eye on him. While there, they discover a growing popularity of a "game that no one can clear" with the other students. Rumors surrounding the Genius Gamer M start to surface as well, as they decide to chase the mystery by finding him. And Sougo and the others end up meeting...? Suddenly, a new Time Jacker, Ora appears!
Tsukuyomi and Geiz learn that 18-year-old Libras have been going missing from Amanogawa High for years and want to check it out, thinking that it's probably an Another Rider plot; Schwartz makes his presence known to Uhr and Ora, forcibly creating a new Another Rider.
Sougo learns of a magic show and wants to check it out. After seeing the magician in action, Geiz believes that he might have been given the powers of Kamen Rider Wizard and wants to fight him.
Uhr gives Kuroto Dan the powers of Kamen Rider OOO, which leads to Kuroto declaring himself king in 2018. Sougo finds common ground with this new Kuroto and wants to learn from him.
Sougo and Tsukuyomi search for Geiz when Sougo notices the news that Team Baron dancers have been disappearing, but Tsukuyomi gets fed up with Sougo constantly returning just after leaving and having an inconsistent memory.
Takeru Tenkuuji and company have been hired by a woman to investigate Another Ghost after her brother mysteriously disappeared; a confrontation occurs with what appears to be Kamen Rider Agito.
With Sougo's soul separated from his body, he guides Takuru back to the year 2015 where Geiz has his Ghost watch taken from him in exchange for a Decade one.
Sougo returns from the future and destroys his belt, ensuring that he will not become Oma Zi-O, but he is later attacked with no one to turn to for help.
Sougo has a dream that he is in the year 2022 and meets a man who goes by Kamen Rider Shinobi. Later, he encounters an Another Rider with the same attacks and a second Woz appears.
Sougo and crew are confused over the appearance of "White Woz"; Geiz and Tsukuyomi try time traveling to get the Kamen Rider Shinobi watch but are forbidden to land.
Sougo and Geiz head into battle with an Another Rider when the original Rider also arrives on the scene. How are both Kamen Rider Quiz and Another Quiz active at once?
Heure breaks a mirror and gives an Another Rider watch to a man inside; Sougo and Geiz have trouble defeating an enemy who keeps retreating even though he has nowhere to run.
Sougo falls asleep while studying and travels 100 years into the future to a world where humans and machines are at war; Tsukuyomi joins forces with White Woz.
Sougo dreams of Kikai going evil while Ora asks White Woz for help with Heure; Geiz asks Tsukuyomi if she really wants to align herself with White Woz.
Tsukuyomi travels back in time to investigate Hiryuu Kakogawa; White Woz tells Geiz that his watch won't activate until he's committed to killing Sougo.
Sougo and crew watch a news report of the G3 unit getting attacked by Another Agito. When they arrive during another attack, Sougo learns that Another Agito is able to multiply and one freezes in front of Tsukuyomi.
Sougo recalls his first love from elementary school; Ora recruits a woman falsely accused of murder to become Another Kiva; a new Kamen Rider falls from the sky.
The Hell Brothers steal the Fourze and Ginga watches so that Sougo and Woz cannot stop the asteroid; Tsukasa takes Tsukuyomi to visit her childhood home.
Momotaros is warned about the demon king by Yuuto, taking back the Den-O watch in the process; the gang must travel back to 2011 to stop the Mole Imagin.
After being defeated by Oma Zi-O, Sougo arrives back in 2019 where all his friends have turned against him and his only ally is a passing through Kamen Rider.
Kamen Rider Aqua arrives in a prototype Time Mazine to take Geiz and Tsukuyomi back to the future; Heure and Ora seek shelter with Sougo after being attacked by Another Drive.
Sougo is given an ultimatum regarding his path by Schwartz and takes Tsukuyomi to visit her own time; enemies that should be defeated because of the previous Kamen Riders are now all returning.
