- Written By: Shogo MutoDirected By: Takayuki Shibasaki
With Ryuga's sacrifice, all seems to be clear. However, our hero and brilliant physicist Sento Kiryu decides to follow up to get Ryuga back from the distortion. What will he find in the distortion, and can he bring Ryuga back home with him?
Episode Tropes:
- 11th-Hour Superpower: The Gold Rabbit and Silver Dragon Fullbottles return during the final battle. While they normally would just make a mismatched Trial form, the fact they are upgraded Hazard Level 7 bottles turns it into a powerful Best Match that helps deal the finishing blow to Evolt.
- Back from the Dead: Or rather, "never died at all." One of the many cathartic things about this episode is showing near everyone who died over the course of the series alive and well due to Evolt's influence being annihilated from the timeline.
- Blunt "Yes": In the final battle, Sento and Evol are pretty much down to their last vestiges of power. Sento in his base form uses the Rabbit and Dragon bottles in his sword for one last attack. Evolt mocks him for it.Evolt: Do you really think that attack is going to work?Sento: (Without a hint of hesitation) I do.
- Book Ends: Two examples:
- The series started on a monologue and from #2 onwards had a recap done by Sento for most episodes. The last episode ends with Sento providing the exact recap from the second episode.
- Ryuga’s fly was down again, just like it was in #1. How long has it been down this time around? Since before they started fighting Evolt. He and Sento even have nearly the same argument on the Machine Builder as they did all the way back in #1.
- Brick Joke: The equations that smash through the Skywall in the opening sequence finally happens in the show as the worlds merge.
- Combat Breakdown: Throughout the final battle, Build is forced to use weaker and weaker forms while Evolt is forced to burn off his energy so that the both of them can keep going. In the end, Sento comes out on top thanks to the Gold Rabbit and Silver Dragon bottles.
- Determinator: Sento’s utter refusal to yield to Evolt causes him to downgrade his main forms each time Evolt tries to bring him down again from RabbitRabbit to TankTank to RabbitTank Sparkling, up until Sento is reduced to RabbitTank.
- Early-Bird Cameo: A sharp-eyed viewer can see the Cross-Z Ridewatch as part of the debris after Sento destroys Evolt for good and the world convergence completes itself.
- Earn Your Happy Ending: Although it seems like no one knows who Sento Kiryu is, everyone that died is now alive and much better off than they were in the Build universe. What makes this especially good for the characters is that even when it seems like they don’t know each other, they found their way back to each other.
- Fighting from the Inside: Ryuga lost his body to Evolt again from dragging him into the spatial distortion, but his presence is still strong enough to hold back Evolt from within until Evolt ejected his encapsulated essence into the Silver Dragon Fullbottle.
- Final Boss, New Dimension: The Final Battle with Evolt takes place inside the rift between the alternate Earths.
- The Greatest Story Never Told: In the new world, no one knows who Sento is or what Kamen Rider Build did to save the world. He and the original Ryuga decide in the end to make an audio journal to avert this.
- Have We Met?: Two examples:
- Sento finds Ryuga in the new universe together with Kasumi, but he has black hair and doesn’t recognize Sento. Kasumi only cements that this Ryuga is different from the one Sento knows when she thinks that he might know Ryuga from his MMA career.
- Misora in the new universe seems to recognize Sento, though unfortunately, it is only because she and Soichi think that he’s Taro Satou of Lynks.
- Hoist by His Own Petard: Evolt releasing the Silver Dragon Fullbottle made it possible for him to be put down for good by attacking Evolt until Ryuga was reawakened. Oops.
- I Should Write a Book About This: At the very end of the episode, Sento hands Ryuga a journal chronicling all of their adventures condensed into 49 episodes, and then decides to start recording an audio journal of himself.
- Leaning on the Fourth Wall: Sento's journal of the series' events are put into a folder that looks suspiciously like a series pitch. And then there's the way he describes them.Sento: I've written down my memories and put it into 49 episodes.
- Merged Reality: The fusion is completed once Evolt was defeated for the last time, combining the Build universe Earth with the alternate universe Earth. It's also heavily implied that this earth is the earth that other Kamen Rider seasons took place on.
- Mythology Gag: Build continues the tradition of defeating the final villain using his base form, though only after hitting Evolt with a Vortex Attack from RabbitDragon.
- Not Quite Dead: Evolt managed to survive being thrown into the distortion and absorbed Ryuga. All that’s left for him is to absorb Sento to restore functionality to his Evol Trigger and ascend to a being without equal. This also has the added consequence of requiring Evolt to be put down once and for all or else the worlds will collide and everything would be for naught.
- Race Against the Clock: Not only is the final battle between Sento and Evolt one to decide if the world will be remade anew, but also one for Sento’s endurance as he’s well past critical condition and bleeding out his golden essence.
- Ret-Gone: Evolt's final fate: as far as the new world is concerned, he never existed. It's unclear is this is simply him having been retroactively destroyed before arriving on Earth in the first place or he was entirely erased, but his influence on the Earth is completely gone.
- Sequel Hook: When he wakes up in the new world, Sento finds the Cross-Z Ridewatch in his hands.
- Shut Up, Hannibal!: Without Genius form, Sento seems powerless against Evolt even without the functionality of the Evol Trigger. Thus, Evolt takes the time to mock Sento, telling him that he's just a fake hero he created. Sento responds back that while Evolt was the one who made him a Kamen Rider, his friends are the ones who created Kamen Rider Build and helped him become a true hero.
- Stranger in a Familiar Land: Sento finds himself alone in Japan after defeating Evolt in the area between the converging worlds, one free of the Sky Wall and apparently where Taizan Himuro is still alive among other changes over 10 years that make it different from the Build universe. Build universe’s Ryuga also ended up in this universe, and even found his black-haired counterpart.
- This Cannot Be!: Evolt is left screaming in disbelief that "puny humans" could destroy him as Sento's final Rider Kick destroys him once and for all.
- This Is a Work of Fiction: The series ends with this message. They probably felt the disclaimer was necessary since the final scene is of Sento having compiled the events of the series into a set of scripts and starting to record the Opening Narration from the first episodes, as if the show we just watched was his resulting account.
- Undignified Death: Formed from the Gold and Silver bottles or no, spiritual Best Match or no, Evolt died not to Genius, the FullFull Bottle forms, Sparkling or even a Best Match. He died to a mismatched Trial Form.
- Villainous Breakdown: Evolt is clearly seething with rage when Sento arrives in the rift and can only stare at him snarling for a few moments. He spends the rest of the final battle noticeably more unhinged than at any other time in the series, making it clear that while he does have a potential way to survive, he's completely furious that he's been brought to the brink of death by "mere humans".
- "Where Are They Now?" Epilogue: After landing in the new world, we see how the cast is doing in their new lives.
- Taizan is Prime Minister of Japan, with Yoshiko and Mido as part of his cabinet, and Gentoku as his aide. Sawa, now just an ordinary reporter, is seen requesting an interview with Gentoku.
- Namba Industries is just a small factory instead of the evil MegaCorp it grew into in the old world. Utsumi is seen working there as a regular factory worker, much happier than before.
- Misora is still running nascita this time with a non-possessed Sokichi. As it turns out, the real one can actually brew a good cup of coffee.
- The Hokuto Trio take Kazumi to nascita, where he falls in Love at First Sight with Misora.
- Ryuga, now with black hair, remains with Kasumi and is still a boxer.
- Taro Satou is alive and his band is thriving.
- As for Sento, he discovers his version of Ryuga exists as a seperate being, and the two ride off together to find their place in this new world.
