- Written By: Kento ShimoyamaDirected By: Ryuta Tasaki
The ordinary high schooler, Sougo Tokiwa, has a future wherein he becomes the overlord and ruler of time, Oma Zi-O.
In order to prevent this, Geiz and Tsukuyomi arrive from the future.
However, Tokiwa Sougo chooses to obtain the power of Kamen Rider Zi-O and defeat Another Build.
Then, Zi-O steals the power of Kamen Rider Build, taking his first step into becoming the Overlor-
Oh my, perhaps I read too far ahead.
Picking up where the pilot left off, Zi-O is under attack by Geiz in his GhostArmor and the Ghost Parkas. Despite this, Zi-O refuses to fight back. Geiz executes an Omega Time Burst Rider Kick to go for the kill, but Tsukuyomi blocks and deflects the kick with Zi-O's Time Mazine, telling the Rider to run away. Zi-O sees a Ridewatch on his wrist with the word "Bike" on it and uses it to summon the Ride Striker to escape. Tsukuyomi tries to block Geiz's path, but he summons his Ride Striker and chases after Zi-O on the road, only for Zi-O to jump off the bike and hide behind a concrete ramp where Geiz cannot see him and continues down the road. Geiz stops and in anger asks why Tsukuyomi why she let Zi-O escape, to which she answers that she isn't sure. Annoyed, Geiz tells her not to interfere again as he must kill Zi-O to save the future.Heure finds the basketball player lying on the ground near a bush and is playing leapfrog over his unconscious body. Heure isn't concerned at Zi-O gaining his power as destined in prophecy, as things can still go according to his plans. He wakes up the basketballer to resume Another Build's reign of terror, first removing the weakened Another Ridewatch from the basketballer's body and restarting it. Heure then re-inserts it to transform the baskeballer back into Another Build.
As Sougo runs home and is nervously looking over his shoulders to ensure none of the people trying to kill him are following, he is greeted by Woz. Sougo demands to know what his deal is and if he is a friend of Tsukuyomi and Geiz. Woz simply states he is the only true ally that Sougo has and that according to his book, the Oma Advent Calendar, Sougo will be destined to rise as the King of Time and ruler of Earth through campaigns of conquest. He also explains that the Time Jackers are trying to stop Sougo's rise to power by attempting to groom others to become the Demon King. Thus, he is the only being trying to protect history as it has been written in his book while all the others are vying to change history. Woz assures Sougo he will do everything in his power to guide his majesty to his pre-destined path in history safely. A shrine gong unfreezes and rings (implying that Woz froze time), and when Sougo turns back to Woz, he sees that the prophet has vanished.
As Tsukuyomi and Geiz search for Zi-O, they hear two baseball players screaming for help as Another Build turns one of them into a Smash Bottle. Tsukuyomi is confused as they already defeated Another Build, but Geiz realizes this means the Time Jackers are in this era and causing trouble. Geiz shows no sympathy for the remaining baseball player, insisting to Tsukuyomi that they leave him to die so they can continue their mission. Tsukuyomi naturally rejects this and Geiz reluctantly decides to help the baseball player by transforming and fighting Another Build.
Sougo finds Woz appearing in his home, who forgot to mention that Another Build is still out there and the Time Jackers have altered history, thus the creature is now Kamen Rider Build. Sougo wonders what happened to Sento Kiryu, but Woz doesn't know. Woz says that as Sougo is now, he cannot defeat Build, though Geiz is trying his best to defeat him. Upon arriving and saving Geiz, Zi-O finds that Another Build has become even stronger thanks to consuming the baseball player's Smash Bottle. He uses his Jikan Girade as a baseball bat to slice and deflect the ball energy projectiles and then asks the two time travelers if they are alright before engaging the monster again. Tsukuyomi wonders if they have got the wrong person as Sougo seems kind and wants to protect them. Zi-O uses his Rider Kick, but Another Build just reappears after being blown up. Sougo thinks he can get help from the real Kamen Rider Build and runs to nascita to find Sento, leaving Geiz to face Another Build on his own.
Soguo goes to the cafe and opens the fridge, only to find the entryway to Sento's lab is gone and the fridge is just an ordinary refrigerator. Sento and Ryuga enter, having returned from a Tsunagiz concert and are acting strange, saying they don't remember meeting Sougo and behaving like morons, with Ryuga calling Sento "Takumi". They claim that nascita is the Tsunagiz Fan Club and have no memories of being Kamen Riders. Meanwhile, Geiz tries to defeat Another Build with his Rider Kick, which causes the two Riders to have their Ridewatches appear and they suddenly remember who they are. Sento and Ryuga remember Sougo and after Sento sees a brief memory from the past in 2017, he entrusts their Ridewatches to him to "give their regards to their past selves".
As he leaves, Sougo at first doesn't get it but soon realizes that Sento was hinting to go back to 2017 to stop Another Build. Geiz is still trying to defeat Another Build in 2018, but he keeps re-spawning every time. Exhausted, Geiz's transformation shuts off and he falls to his knees. Sougo runs back and gives Geiz the Cross-Z Ridewatch,saying they need to go see Kamen Rider Build in 2017 to stop Another Build. Both of them get into the Time Mazines and jump to 2017, where Another Build is terrorizing the citizens. The monster turns two students into Swimming and Archery Smash Bottles before deciding on attacking Ryuga and Sento in the past. The two notice the monster isn't a Smash, but know they need to try to stop it. They both transform into Kamen Rider Build and Cross-Z, but their efforts are no good. Time distortions cause the power of their Drivers to flux as their powers fade in and out of temporal existence due to the presence of the evil Build, with the phony Rider's latest Smash Bottles boosting its power and agility to overwhelm them. The Time Mazines ram Another Build and the two Riders try to meet up with Sougo and Geiz, only to be frozen by Heure. Heure insists that Zi-O not interfere with his plans to create a new king before taking his leave.
Sougo and Geiz transform, which unfreezes Build and Cross-Z. The quartet of Riders try to fight briefly together, but Build and Cross-Z's powers fade away from time. Zi-O uses his Build Ridewatch to summon the BuildArmor and equips it. He then works with Geiz using the Cross-Z Ridewatch to do a double finisher to finally take down Another Build.
Upon the defeat of Another Build, the Another Ridewatch shatters and the basketballer awakens back in 2017 with no memory of what happened. But his fate was still altered as the cars still crashed into each other and the black one did not hit him. Sougo tries to return Ryuga and Sento's Ridewatches to them after Geiz mentions that they didn't have them in this time (thereby creating a time loop where either way Sougo gets the Ridewatches). But Sento Kiryu no longer exists as Takumi Katsuragi is in control of Sento's body, but shows interest in the now sealed Ridewatches. Ryuga refers to him as Takumi too. The attempt to restore history had failed, but Sougo believes that Sento will come back and choose to be Kamen Rider Build again someday. The two fly off in their Time Mazines back to 2018, with Takumi and Ryuga witnessing this as Sougo waves goodbye to Takumi in his Time Mazine.
Later that night, Geiz and Tsukuyomi wonder if Sougo truly is the future Demon King based on his heroic actions. Geiz thinks Sougo will still become the evil Zi-O based on the fact he has gained Build's powers and Kamen Rider Build has been erased from history, thus the events that led to the bad future they live in are already set into motion. Sougo wakes up the next morning only to find that his uncle has found a renter for the second room in the house and that it is Tsukuyomi and Geiz who are going to be living with him. Tsukuyomi makes it clear that they are just observing him and Geiz whispers to Sougo that he will kill him if given the chance. The trio sit down to an awkward breakfast, with Sougo telling his uncle they will all try to get along as roommates.
As Woz reads from his tome, a familiar hospital hallway is shown with a doctor walking towards the pediatrics ward, revealing to be Emu, also known as Kamen Rider Ex-Aid...
Episode Tropes:
- Borrowed Catchphrase: When Sougo accesses the BuildArmor for the first time, Sento tries to teach Sougo his catchphrase, only for Sougo to flub it to Sento's dismay.
- Series Continuity Error: Interestingly, Zi-O's Build canon, and Build's canon don't line up, whereby the event of Sento gaining the Cross-Z Ridewatch in the final episode of Build is not mentioned at all, instead showing the origins of the Build and Cross-Z Ridewatches being Sento and Ryuga gaining their memories back.
- The Cameo: Sento and Ryuga appear in this episode once again, both in nascita in 2018, losing their memories and becoming avid fans of reviving Sato Taro's old band, and in 2017, where Sougo gains BuildArmor.
- Funny Background Event: Sougo tries to do the equation flood that Sento makes whenever he shakes a Fullbottle and gets serious, only to create random sentences that feel like they were the first thing that came to mind.Ryuga: That don't seem right.Sento: This is terrible.
- Have We Met?: Another Build's presence on the timeline causes Sento and Ryuga to forget about Sougo and their Rider powers, which only recedes temporarily whenever Another Build is defeated.
- Nice Job Breaking It, Hero: Because of Sougo, Geiz and Heure's interactions with the past, Sento and Ryuga no longer have their powers left, and Sento doesn't recognize his own name anymore, referring to himself as Takumi Katsuragi.
- Stable Time Loop: When Geiz points out that Sougo wouldn't be able to get Build and Cross-Z's Ridewatch in 2018 since they dealt with Another Build in 2017, Sougo gives Sento and Ryuga blank Ridewatches that would eventually contain their powers to make sure that he could use them when the time comes.
His path of conquest had only begun.
However, his meeting with another legend was already at hand...
