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Now, shall we begin the experiment?note 
"Ten years have passed since the Pandora Box was discovered on Mars and caused the infamous Skywall Incident. Our country was divided into three districts known as Tōto, Seito, and Hokuto, resulting in utter chaos."note 
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Kamen Rider Build is the 2017-2018 entry in the Kamen Rider series; the nineteenth entry in the franchise's Heisei era, and the twenty-eighth entry overall.

Ten years ago, Japan launched Project Prominence: the first successful expedition to Mars. If that wasn't enough, the astronauts managed to bring back with them proof of extraterrestrial life on the red planet - a mysterious cube with strange properties, found in ancient ruins. This artifact holds the potential of discovering a source of unlimited clean energy. With this incredible asset in their hand, all signs pointed at the advent of a Golden Age for Japan. But then everything went wrong.

During the celebration of the expedition, where the cube was for the first time shown to the world, a mysterious man barged in and, after a struggle with security, reached out and touched the object. This resulted in its activation and caused the sudden appearance of the Skywalls - giant, crimson-glowing walls that violently tore through Japan, and even reached miles into the sea. Not only that, everyone present at the event were warped by the energies of the cube, increasing their inherent aggression. This resulted in the nation being divided into three opposing states - Tōto, Seito, and Hokuto.note . Each one with a separate government and doctrines, but all desiring the massive power of the artifact - which after the Skywall disaster became known as the "Pandora Box" - for themselves.

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In the present day, Tōto holds custody over the Pandora Box, but a new crisis shakes the region - the appearance of humans-turned-monsters known only as "Smash". While the government evades the topic, there is a hero hunting down the beasts. Unbeknownst to all, his identity is a young, amnesiac genius physicist named Sento Kiryū, who was taken in by café owner Sōichi Isurugi when he was found in a rainy alley with no memories of anything except his escape from experimentation on by an evil organization called Faust. Now, as he searches for clues about his past, he uses the Build Driver to transform into Kamen Rider Build and personally combat Faust and the Smash, his powers augmented by "Fullbottles", bottles containing essence of Smash purified by Misora Isurugi, Sōichi's mysterious daughter.

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It premiered on September 3rd, 2017, after Kamen Rider Ex-Aid finished its run; and it aired alongside Uchu Sentai Kyuranger, and later, Kaitou Sentai Lupinranger VS Keisatsu Sentai Patranger, on the Super Hero Time block. It ended on August 26, 2018, and was succeeded by Kamen Rider Zi-O.

Kamen Rider Build's tie-in projects include:

  • Kamen Rider Heisei Generations Final Build And Ex Aid With Legend Riders, the annual crossover movie; here featuring Kamen Rider Ex-Aid as Build's co-star.
  • Kamen Rider Build: Birth! KumaTelevi!! VS. Kamen Rider Grease!, a Televi-kun magazine exclusive DVD special featuring Build's KumaTelevi Form.
  • Kamen Rider Build: Raising the Hazard Level ~7 Best Matches~, a web series that features seven Best Matches not seen in the show.
  • ROGUE, a miniseries featuring Gentoku Himuro's transition from Night Rogue to Kamen Rider Rogue, exclusive to the DVD collections.
  • Kamen Rider Build Be The One, Kamen Rider's requisite Summer movie.
  • Kamen Rider Prime Rogue, a Televi-kun magazine exclusive DVD special centering on Gentoku Himuro/Kamen Rider Rogue.
  • Kamen Rider Heisei Generations FOREVER, the next crossover with Kamen Rider Zi-O.
  • Kamen Rider Build NEW WORLD, a series of DVD movies set after the end of the series, focusing on secondary Riders.
    • Kamen Rider Cross-Z
    • Kamen Rider Grease

There exists a character sheet and a recap page for the series. Please place any related tropes there.


Recurring Kamen Rider tropes include:

  • Catch-Phrase: Lots. Before transforming, Sento/Build says, "Now, shall we begin the experiment?" When switching forms, he announces, "Build Up!" When he gains an advantage, he says, "The laws of victory have been decided!" or, "I've found the winning formula!" depending on the subtitler. As Cross-Z, Ryūga's is, "I've got the feeling I can't lose!" As Cross-Z Magma, he says, "My power is overflowing, my soul is burning, and my magma is surging!" Kazumi/Grease has "The fire of my heart... passion..." and "I'll crush you with the fire burning in my heart!" Gentoku/Rogue's is "You will be a sacrifice for the greater good."
  • Cool Bike: Build has the Machine Builder, a motorcycle that transforms from a smartphone when it's loaded with a Fullbottle. The Lion Fullbottle is the default Fullbottle for this, but another Fullbottle will do in a pinch.
  • Early-Bird Cameo: Build first made appearances in Kamen Rider Ex-Aid the Movie: True Ending and in Ex-Aid episode 44; in the latter he tried to get a sample of Ex-Aid's power but mistook Genm for him instead, leading to a fight.
    • The Kaiser-type enemies, Build's PhoenixRobo Form, and Kamen Rider Grease all first appeared in Kamen Rider Heisei Generations FINAL: Build & Ex-Aid with Legend Riders.
  • Finishing Move: Naturally, there are a ton of these, so we won't list them all. They generally follow the pattern of "____ Attack", "____ Break", and "____ Finish"; with "Finish" being the strongest and the "___" part unique to the Rider or form.
    • Build has "Vortex" moves; "Vortex Finish" moves in Best Match forms, "Vortex Break" when using the Drill Crusher, and "Vortex Attack" while in mismatched Trial Forms. Finishers for upgraded forms tend to swap "Vortex" for the name of the upgrade: "Sparkling Finish", "Hazard Finish", "Genius Finish", etc. The Fullbottle Buster also uses "Break" finishers depending on how many Bottles are used: Fullbottle Break, Just Match Break, Miracle Match Break, and Ultimate Match Break; plus the FullFull Match Break when using the FullFull RabbitTank Bottle.
    • Cross-Z uses "Dragonic" finishers normally, "Great Dragonic" as Great Cross-Z, and "Volcanic" as Cross-Z Magma. His Beat Closer sword has "Slash" attacks: Smash Slash, Million Slash, and Mega Slash. As Cross-Z Charge, his finisher names are the same as Grease's. Cross-ZEvol can use the Muscle Finish, Galaxy Finish, and Muscle Galaxy Finish.
    • Grease has "Scrap" finishes normally and "Glacial" as Grease Blizzard. He can also use Charge Crashes and Discharge Crashes depending on whether an organic or inorganic Fullbottle is crushed in his Sclash Driver, and the Twin Breaker allows its user to perform a Single/Twin/Let's Finish or Break depending on what is inserted in which mode.
    • The Transteam Gun and Steam Blade perform various "Steam" attacks, while the the Nebulasteam Gun labels its attacks as "Funky".
    • Kamen Rider Evol uses "Evoltic" finishers in his regular form and "Black Hole" finishers in Black Hole form.
    • Be the One notably turns the series' Arc Words into a finisher, with Cross-ZBuild performing a Love and Peace Finish.
  • Henshin Hero: If you're expecting something else at this point, you might as well give up.
  • Home Base: Sento and Ryūga's hideout is located beneath café "nascita", which doubles as Sento's lab. The entrance is hidden behind a fake refrigerator.
  • Humans Are the Real Monsters: Played With throughout the series.
    • It's clear from the start that the Smash are just innocent victims of horrific experimentation; the real evil are those doing the experimenting. However, one of them is genuinely trying to protect his faction and turned to extreme measures, unwittingly under the influence of the Pandora Box. The other is a malevolent anarchist who is revealed not to be even human. The original founder of the experimentation initiated thinking it was necessary as he was trying to take down the latter.
  • Merchandise-Driven: Another Toku show, another set of toys to sell. This series' focus is on the Fullbottles.
  • Monster of the Week: Smash, monsters born from human experimentation by Faust. Like Kamen Rider Gaim and Kamen Rider Ex-Aid, though, the main threat is from evil Riders, with the kaijin being more treated like Elite Mooks.
  • Multiform Balance: Build follows the Kamen Rider OOO model here, with specific combinations ("Best Match"es) being stronger and given more focus.
  • Phlebotinum Rebel: With the twist that rebelling is much more difficult than normal. Sento, Misora, and Ryūga are all Faust escapees who use stolen Faust tech to fight their former captors, but continually find that their efforts to rebel are just another part of Stalk's schemes, as he takes advantage of their heroism to benefit himself. It's not until late in the show that they finally start to find ways to truly slip out of his control.
  • Sixth Ranger: The secondary rider is Kamen Rider Cross-Z (pronounced "Crozz"; the Z is incorporated into the syllable rather than being pronounced separately). Later on, Kamen Riders Grease and Rogue joins them.
  • Transformation Trinket: The Fullbottles are the source of power, which characters use various devices to access.
  • Kamen Rider Build uses two Fullbottles at once in the Build Driver, one with a organic power and one with inorganic. The Fullbottles tend to be grouped by their region of origin:
  • Kamen Rider Cross-Z gets a number of different trinkets himself:
    • To start, he uses the Dragon Fullbottle with the Build Driver and an add-on called the Cross-Z Dragon.
    • He soon switches to the Sclash Driver, which uses gel packets called Sclashjellies, for a form utilizing the Dragon Sclashjelly called Cross-Z Charge.
    • After the Dragon Jelly is destroyed, it's modified into a new Dragon Magma Fullbottle that Cross-Z uses with the Build Driver and a different add-on, the Cross-Z Magma Knuckle, to become Cross-Z Magma.
    • He also steals Evol's Dragon Evolbottle and uses it with the Cross-Z Dragon (transforming them into the Great Dragon Evolbottle and the Great Cross-Z Dragon in the process) for one more form, Great Cross-Z. This is largely a replacement for Cross-Z and Cross-Z Charge, which were no longer accessible at that point.
    • In NEW WORLD: Cross-Z he gets a brand-new Cross-ZEvol form thanks to the Muscle Galaxy Fullbottle, a remodeled Genius Fullbottle.
  • Kamen Rider Grease also uses a Sclash Driver, only with the Robot Sclashjelly. In the final episodes, he adopts a Build Driver and a Grease Blizzard Knuckle add-on with a North Blizzard Fullbottle, becoming Grease Blizzard. He gets one more (currently unknown) form in NEW WORLD: Grease, which uses another add-on called Perfect Kingdom and a new, enhanced version of the Robot Fullbottle.
  • There's a fourth group of man-made Fullbottles besides those of the three regions, called Lost Fullbottles. These include Bat, Cobra, Castle, Kuwagata (Stag Beetle), Fukurō (Owl), CD, Shimauma (Zebra), Hasami (Scissors), Hammer, and Spanner. They're used by Faust agents in various ways across the show:
    • Night Rogue and Blood Stalk use the Bat and Cobra Lost Fullbottles respectively with Transteam Guns.
    • The Hokuto Three Crows each use their Lost Fullbottles on their own to become Hard Smash: Castle, Kuwagata (Stag Beetle), and Fukurō (Owl).
    • Late in the series, the Lost Fullbottles can be used in conjunction with two Clone Smash and a human host in order to create a Lost Smash.
    • In Be the One, two Blood Tribe members use Shimauma and Hasami to become the Zebra Lost Smash and the Scissors Lost Smash. The third uses the Cobra Lost Fullbottle with the Hazard Trigger and Cross-Z's Great Cross-Z Dragon add-on, plus physically merging with the first two and Ryūga, to become Kamen Rider Blood.
  • Night Rogue eventually, like Cross-Z, upgrades to a Sclash Driver, using a "Crack" variation of a Crocodile Fullbottle instead of a Sclashjelly to become Kamen Rider Rogue. In Kamen Rider Prime Rogue, he gets a new Prime Rogue form with a Build Driver and a FullFull Bottle called the Prime Rogue Fullbottle.
  • The Kaisers use Nebulasteam Guns with "Gear" Fullbottles. Both the ones from Heisei Generations FINAL and Seito's Hell Bros use the same powers in different colors; with one of the pair one using Gear Engine and the other using Gear Remocon (Remote Control).
  • Blood Stalk also upgrades to becoming Kamen Rider Evol, using a unique belt and Fullbottles called the Evol-Driver and Evolbottles. He uses Cobra and Rider Evolbottles for his main form, but can switch Cobra out for Rabbit or Dragon Evolbottles when possessing Build or Cross-Z to mimic their powers. He also has an Evol-Trigger add-on that changes him to Black Hole form.
  • Kamen Rider MadRogue (who is a different person from Night Rogue/Kamen Rider Rogue) uses an Evol-Driver and transforms with Bat and Engine Fullbottles (normal ones, not the Bat Lost Fullbottle or the Gear Engine).
  • Near the end of the series, the Rabbit and Dragon Fullbottles change colors (becoming the Gold Rabbit and Silver Dragon Fullbottles) due to their main users reaching Hazard Level 7. In Be the One, they combine with the Genius Fullbottle into the Sparkling-like Cross-ZBuild Can that creates a Double-like Fusion Dance, Cross-ZBuild. They return in the series finale, where Sento uses them to create a gold/silver RabbitDragon form.
  • In Kamen Rider Cross-Z, Evol's older brother Kamen Rider Killbas debuts, using the Killbas Spider Fullbottle and a Killbaspider add-on in the Build Driver.
  • Weapon of Choice:
    • Just as Build has several forms, he gets several weapons to go with those forms:
      • The Drill Crusher, which switches between drill (or rather, drill-shaped sword) and gun forms. This is his default weapon and is not tied to any specific form.
      • Gatling forms get, of course, a gatling gun called the Hawk Gatlinger.
      • Ninjya and Comic forms use a Cool Sword called the 4-Koma Ninpōtō; which activates ninja techniques of duplication, fire, wind, and smoke bombs.
      • For Kaizoku forms, he has the Kaizoku Hassyar bow.
      • RabbitRabbit and TankTank have the Fullbottle Buster; another sword/gun combo but much bigger.
    • Cross-Z has his own Cool Sword, a music-themed blade called the Beat Closer (though can be used by anyone else using the Dragon Fullbottle too). As Cross-Z Magma, he gets the magma-based Cross-Z Magma Knuckle Power Fist (though he can use it as regular Cross-Z as well). Later in the series Sento creates the ice-element Grease Blizzard Knuckle as well, which Grease uses to access his 11th-Hour Superpower Grease Blizzard.
    • Grease and Cross-Z Charge both use a wrist blaster/Pile Bunker hybrid weapon called the Twin Breaker. Grease's first upgrade allows him to wield both of them.
    • Night Rogue and Blood Stalk each have a Transteam Gun and Steam Blade, which can combine to form the Steam Rifle. Both continue using them after upgrading to being Kamen Riders, as does MadRogue.
    • The Kaisers and Kamen Rider Rogue use updated Transteam Guns called Nebulasteam Guns, which can also be combined with the Steam Blade to form the Nebulasteam Rifle.

Kamen Rider Build provides examples of:

  • After the End: The End being a Type 1 Regional Apocalypse caused to Japan (skirting Type 2 in Hokuto).
  • Alien Invasion: It's eventually revealed that the entire plot is a one man invasion by Evolt, who seeks to wipe out all life on Earth like he previously did Mars.
  • Aliens Speaking English: Justified in the case of Vernage, who explains that seven years was more than enough time for her to learn Japanese. Less justified with Evolt, who spoke fluent Japanese immediately upon arrival, and whose Evol-Driver speaks Gratuitous English and Gratuitous Italian despite existing since before the dawn of life on Earth.
  • Alternate Universe: Build is the first series to not use the Shared Universe concept established by Decade at the turn of the millennium, presumably because nobody would buy a Hand Wave like "Japan's been split in three since 2007, we just never brought it up before now". Confirmed by Heisei Generations FINAL, which has this series take place in "the World of Build", suggesting a Decade-style parallel universe.
    • This comes back in a big way in the final arc, where Sento discovers that his father's plan for defeating the seemingly invincible Evolt involved safely merging the "World of Build" with a parallel Earth (implied being the main Kamen Rider universe) where the Skywall Disaster had never happened. Evolt and the Pandora Box would supply the unfathomable amount of energy required for the merger, which would theoretically cause both to cease to exist. In the final episode the plan succeeds, producing a new world that has the Build cast but none of the events of the series have happened, while Sento and Banjō, who were created by Evolt's machinations, still exist but nobody remembers them.
  • Apocalypse How: The Skywall Disaster was a Regional Type 1. Japan's society as they know it has been more or less completely destroyed, resulting in a more dystopian situation in all three capitols. Hokuto is skirting a Type 2 as the Skywalls altered the soil, causing a famine and economic collapse.The destruction of Mars was a Class 6 resulting in the complete annihilation of the Martian civilization, leading Mars to become the lifeless rock it currently is. And it's implied that the cause of this was the Pandora Box opening fully.
    • At full power, Evolt has the ability to pull off Class X apocalypses at will by creating black holes that he uses to suck up planets; in one episode he forces Sento to watch while he wipes out an alien planet in an attempt to demoralize the hero. He almost pulls a Class X on Earth in the final arc, but the heroes find a way to turn it around on him.
  • Applied Phlebotinum: Nebula Gas, supposedly emanating from parts of the Skywalls' own foundations, and thanks to Takumi Katsuragi's research, able to mutate people into Smash.
  • Arc Words: As the show goes on, the Build Driver's intense "ARE YOU READY?!" slowly turns from a silly toy jingle to a confirmation of Sento's will to keep going even as everything goes wrong. First seen after he finally gets over the reveal that he is actually Katsuragi the Devil Scientist, then when he decides to keep fighting as Build for the sake of his friends even through his PTSD-level terror of the Hazard Trigger's effects. When it's used like that, the voice clip usually gets the time to echo into the distance instead of going straight to the rest of the transformation.
    • "Love and Peace". Sento declares that this is what he fights for as Kamen Rider Build, and it ends up resonating with Ryūga, Kazumi and even Gentoku. A driving theme of the show is whether or not it's even possible to achieve such things as the situation gets worse and worse and whether it's even worth it. The movie reveals that Sento got this ideal from his father Shinobu, and that it was the reason he became a scientist.
  • Artifact of Attraction: While the Pandora Box being a potentially super powerful energy source is one reason everyone wants it, the way Gentoku talks about it implies it's more than that and it's in some way actively compelling those infected by its Hate Plague to desire to claim it as their own and use it to Take Over the World or unknowingly destroy it.
  • Artifact of Doom: The Pandora Box, which was discovered on Mars and taken back to Earth. When opened, it released the Skywalls and increased the aggression of everyone present at the event, both of which led to Japan's balkanization. It also ruined Hokuto's soil, but only Hokuto's, seemingly with the deliberate intent of causing it to become an aggressive police state. All of this is only the beginning of the doom the Box inflicts, though: the Skywalls themselves emit Nebula Gas, used to create Smash and from them Fullbottles. At the same time that the Box created the walls, it released six panels from its various sides, meant to be filled with Fullbottles and reattached to the Box. Doing so causes the Skywalls to begin to transform with each new panel attached, forming into a tower. When the Pandora Tower is finished, the world ends.
  • The Bad Guys Are Cops: Because both Ryūga and Sento are on the run, they must often fight against Tōto's Guardian forces while dealing with Smash. At least before the war with Hokuto begins. Now they're must fight together with Gentoku/Night Rogue to protect Tōto.
  • Balkanize Me: Due to the appearance of the Skywalls and the adverse mental effect it had on the politicians at the event, Japan got split both literally and metaphorically into three different states, each with their separate governments and doctrines. Reality Ensues, as the balkanization of Japan has made it extremely weak on an international level, and the threat of foreign invasion or domination is brought up as a pressing concern. The new nations are:
    • Tōto (Eastern Capital), set around eastern Honshū. They adhere to traditional pacifism and is the main setting of the show.
    • Hokuto (Northern Capital), consisting of Hokkaidō and northern Honshū. While allegedly focused on social welfare, most of their efforts have instead gone into developing their military power at the expense of their citizenry.
    • Seito (Western Capital), with a territory made of Shikoku, Kyūshū and western Honshū. They pursue economic recovery in face of the incident.
  • Beware the Superman: Night Rogue and Blood Stalk have comparable power to Build and are Rider-like in nature. The show makes zero attempts to hide how absolutely terrifying the concept of an unfettered, psychopath with with punches and kicks in the double digit tons of force would be to go up against if you're a normal human. On several occasions, normal human soldiers are pitted against them and are easily slaughtered. The best example of this would be in episode 11 when Blood Stalk back hands a human guard in the face and obliterates him, then effortlessly dissolves a second with his venom, doing so with almost casual ease. To make matters worse, Night Rogue's ultimate plan is to mass produce Kamen Riders as Super Soldiers...
  • Beyond the Impossible: The movie reveals that when a person reaches Hazard Level 7, the Fullbottle that resonates the most with them undergoes an incredible transformation, as seen in the final arc with the Rabbit and Dragon Fullbottles becoming gold and silver respectively. In this state, the Bottles can break the pre-established rules of the Build Driver and access (namely, the "one organic and one inorganic Fullbottle" requirement), allowing a user to assume an incredibly powerful Rider form that defies the Laws of Physics. This is seen in the movie with Build Cross-ZBuild Form and in the final episode with Build RabbitDragon Form.
  • Big-Bad Ensemble: Five separate villainous factions emerge, each with their own agendas:
  • Big Good: Vernage, the Queen of Mars. She actively protects the heroes several times, provides the clue needed to control the Hazard form, and warns the heroes about Evolt, the destroyer of Mars. In fact, she's the only reason that the heroes got a chance to fight him at all: she drained the Fullbottles in the Pandora Box so Evolt couldn't just instantly destroy Earth the moment he arrived.
  • Bittersweet Ending: Sento's plan succeeds, destroying Evolt and creating a new world where the Skywall Disaster never happened. Everyone now has peaceful, happy lives and those who died are alive and well... but Sento is now an anomaly since he was a creation of the old world, meaning nobody remembers him and he doesn't have a place in the new world either as Takumi Katsuragi or Tarō Satō. Vernage disappears after Evolt's defeat and Takumi Katsuragi's consciousness fades for good. However, Sento ends up finding the original Banjō, who's in the same boat as Sento since he was made with Evolt's DNA (meaning there's another, 100% human Banjō in this world), and the two set off to find a place in the world, planning on telling the story of Kamen Rider Build as a TV show. The last scene is a humorous beat with Sento giving the first narration we heard at the beginning of the season.
  • Book-Ends:
    • With the abdication of Emperor Akihito on April 19, 2019, Build is almost just in time to be a Meta example, providing one for the entire Heisei Era Phase 2, being a Rider with a Half and Half design similar to Kamen Rider Double who solves mysteries (Shōtarō) and collects data while trying to remedy his amnesia (Phillip). The series after Build, Kamen Rider Zi-O, is a Milestone Celebration like Kamen Rider Decade, providing a different form of Book End.
    • Likewise, the series' plot is the result of an expedition unearthing something evil while exploring the ruins of a long-extinct, previously unknown civilization, just like the first Heisei Era Rider series, Kamen Rider Kuuga.
    • An internal version: In Episode 14, Sōichi calls Sento to the alley where they met in the first place and Sōichi "found" the amnesiac Sento one year prior. The battle goes into a nearby warehouse but ends right back in the alley, where Sento declares "The man I knew as Sōichi Isurugi is dead."
    • Another internal example: The first and last episodes both end the same way: As "Be The One" plays, Sento and Banjō ride tandem on the Machine Builder. Sento points out that Banjō's fly is open, and has been since the last battle; Banjō gets mad at him for not saying anything earlier and starts shaking him after Sento calling him "idiot", causing Sento to panic that he's going to make them fall over.
  • Boss Rush: The ascent up the Pandora Tower in the final few episodes is this, seeing the Riders have to fight clones of the Hokuto Three Crows, then the Kaiser Bros, then Evolt himself as Evol Cobra before finally facing Evol Black Hole, then Evolt's One-Winged Angel form at the top.
  • Brains and Brawn: Genius physicist Sento and former pro-fighter Ryūga.
  • ...But He Sounds Handsome: Sento exhibits this when he serves as the narrator, recapping the events of last week's episode. He calls himself a "hottie and brilliant physicist" and deliberately plays up his more virtuous characteristics, as well as exaggerating Ryūga's more negative aspects.
  • Call-Back: Episode 46 opens with Evolt-as-Midō delivering the original opening narration (quoted at the top of the page) as part of a televised speech.
  • Cerebus Retcon: Many of Build’s bizarre choices for Best Matches are simply accepted by the protagonists, with things from Turtles and Watches to Pirates and Trains, are revealed to be the result of Sōichi telling Evolt 30 things his daughter loved, and then Evolt wanting 30 things that could destroy them. While Sōichi initially went along with it (hence Tank, Gatling, and the like), he started making more nonsensical suggestions like Erasers and Comics out of a desire to protect what Misora loved, and thus resulted in the Best Matches.
  • Chekhov's Boomerang: The Hazard Trigger starts off as just a means to give Build his Next Tier Power-Up (and to add some drama with its making him go berserk). However, Sento begins questioning if that's all there is to the Trigger, since he can't fathom someone inventing a "berserker machine". Near the end of the series, a dying Shinobu Katsuragi reveals to Sento that it's the key to beating Evolt — not only can it purify the Lost Fullbottles, but it creates a white Pandora Panel that's key to Shinobu's plan to merge Build's Earth with a parallel Earth that will destroy Evolt in the process.
  • Chekhov's Gun: Some of the Fullbottles seen early in the series (notably both Night Rogue and Blood Stalk's Bat and Cobra, or the Hokuto Three Crows' Owl, Beetle and Castle) are weirdly mismatched compared to the rest, made of brown plastic and filled with purple gas, compared to a regular Fullbottle's black base and uniquely colored contents. Most of them aren't even part of a Best Match, even (Bat is the lone exception... but there's a standard Bat Fullbottle and it looks completely different). No attention is paid to them, until the very last stretch of the series, where they turn out to be the Lost Fullbottles, a particular set that when gathered can enable wormholes and even pan-dimensional travel, and are one of the most important plot points of the final arc.
  • Civil War: The first act of the series is the long, slow buildup to one: the peace between the three capitols is paper thin, and with the exception of Tōto, the prime ministers are just looking for an excuse to break it. It's ultimately Night Rogue and Nanba's goal to set off the powder keg and start a Japanese civil war for their own ends. By the end of the first act, they succeed, and the second act deals with the war itself in all its horrors.
  • Combat and Support: The team dynamic in the last quarter largely involves dividing the riders into two teams. Build's upgrades and Cross-Z's ever increasing power serve as the combat team, dealing most of the damage in a fight. Support is provided by Grease and Rogue, who frequently serve to distract or stall enemies and give the other team an opening to attack.
  • Combat Breakdown: In the final episode, Sento has lost Genius Form because the Genius Fullbottle was part of the setup required to merge the worlds. When he chases Evolt down to get Banjō back, his most powerful forms are RabbitRabbit and TankTank; over the course of the battle he drops back down into RabbitTank Sparkling and then finally to the original RabbitTank. However, he then gets an 11th-Hour Superpower by using the Gold Rabbit and Silver Dragon Fullbottles to assume RabbitDragon Form for one final Rider Kick that finishes Evolt once and for all.
  • Combat by Champion: Hokuto and Seito had challenged the Riders of Tōto on separate occasions to this.
  • Combo Platter Powers: Build uses the same style of powers as Kamen Rider Double, where two different items are used at once and the resulting form has aspects of both. In this case, all forms are a mix of something organic and something inorganic.
  • Continuity Nod: As seen in Heisei Generations FINAL:
    • Gentarō is already a teacher, in accordance with Movie War Ultimatum which shows the Kamen Rider Club 5 years in the future. While in reality it's been a bit longer than that, it's been stated that Heisei Generations FINAL occurs one day before Movie War Ultimatum.note 
    • Likewise, Kouta is already a space god in this movie.
  • Cosmic Horror Reveal: At the start, the plot seems to be about trying to stop an evil syndicate in a Balkanized Japan following an apocalyptic disaster. While definitely a scifi story, the villains are humans doing rotten things who create monsters with experiments, and even the second arc is a War Arc with the same base ideas... then it's revealed that everything is being orchestrated by a planet destroying Ancient Evil spirit accidentally released from the last planet he destroyed predating life on Earth who's been possessing the astronaut who unearthed him since then.
  • Cosmic Horror Story: As the show continues, its story beats match up pretty perfectly to one. An ancient alien artifact is found on the Once-Green Mars and brought to Earth, where it's opened by the astronaut who found it who's now possessed by an ancient evil spirit predating life on Earth and seeking the destruction of all life on Earth and releases walls that split Japan into three parts that release gas that turns humans into rampaging monsters, as well as an energy that warps the minds of everyone present to become amoral war mongers, compelled to fully open it and release whatever lies inside. Which is The End of the World as We Know It, which is what happened to Mars. Oh, and it turns out Ryūga was born thanks to an alien that hitched a ride on a Mars probe and isn't even fully human.
  • Darker and Edgier: Most Kamen Rider series for the past few years had been fairly lighthearted, with a few (like Kamen Rider Gaim, Kamen Rider Drive, and Kamen Rider Ex-Aid) taking a turn for the worse later. This one starts out with unethical human experimentation, an innocent man being framed for murder and goes from there. Only Kamen Rider Amazons trumps Build in terms of Downer Beginning, and that one was specifically geared towards adults. The final arc deals with facing an Ancient Evil who's a walking extinction event.
  • Deadly Upgrade: It is possible to forcibly raise a person's Hazard Level with infusions of raw Nebula Gas. Doing so is likely to kill the subject outright. Those who survive will have their Hazard Level raised so high that the shock of a defeat in battle or even exposure to particularly strong doses of purified Nebula Gas will prove fatal.
  • Department of Redundancy Department: Riders since Kamen Rider Gaim have had Legend Rider form changes, which give them costumes based on previous Riders, but in the current Rider's aesthetic. Rather than have unique costumes, Build's Legend Rider Best Matches cause him to turn into the past Rider outright while retaining his own belt. This includes being able to turn into Decade, whose gimmick was that he could turn into any past Rider while retaining his own belt.
  • Detonation Moon: In the penultimate episode, Evolt absorbs Earth's moon into a black hole, making him even stronger.
  • Double-Meaning Title: The movie Kamen Rider Build Be The One. It's a reference to the idea of being the one everyone looks up to, and Ryūga and Sento's Super Mode that requires them to fuse; in other words, "Be the One".
  • Dramatic Irony:
    • The audience is made aware of Night Rogue's true identity long before the characters figure it out.
    • Sōichi being possessed by Evolt is revealed to the audience, but the characters remain unaware of that fact and believe Sōichi was a heartless man who used Sento and his own daughter.
  • Dug Too Deep: The Pandora Box was unearthed by an expedition to Mars and brought to Earth, resulting in it releasing the Skywalls and setting in motion a series of events that could potentially cause the end of the world. The expedition also released an Ancient Evil spirit that possessed Sōichi, namely Evolt, the destroyer of Mars, who'd been stuck stranded on Mars for millions of years.
  • Dwindling Party: In the two episodes before the finale, the heroes lose Kazumi, Gentoku and Ryūga over the course of their final battle with Evolt.
  • Eldritch Location: The Pandora Tower is this, in addition to being a world-ending superweapon. the insides of the tower make no sense compared to the tower's dimensions and can be shifted about by Blood Stalk via the Pandora Box itself, which can range from simply manipulating the material on the inside to creating the illusion that the people inside are in an outdoors location.
  • Evolving Credits: The opening changes with Episode 29, with the narration (quoted at the top of the page) now reflecting the shift in arcs and the addition of Kazumi, Sawa, Sōichi as Blood Stark and even Katsuragi. The narration changes again with Episode 36, reflecting the presence of Evolt and the fact that the Pandora Box has been opened, and Sōichi's transformation into Blood Stalk is eventually replaced with him becoming Evolt instead. However, some things strangely don't change when you'd expect, such as Cross-Z Charge remaining in the opening to the very end even though that form is permanently destroyed mid-season. His later modes such as Cross-Z Magma and Great Cross-Z never appear in the opening, in favor of that long-gone form. Most notably, Magma is his strongest form, the only one used in the last eight episodes, and appears in far more episodes than Charge.
  • Exact Words: It was stated that Kamen Rider Build Be The One happens after the Japanese Civil War. This caused many people and sources to think it took place after the series, but in Episode 42 Evolt destroys the Tōto government thus ending the civil war in Seito's victory.
  • Fantasy Helmet Enforcement: Helmets being pulled out of nowhere is justified, as the first episode shows that the Machine Builder has an app that can make a helmet materialize for anyone riding to wear.
  • Felony Misdemeanor: Used as a plot point, of all things. When directly attacking Seito's forces becomes diplomatically too complicated, Sento and Prime Minister Himuro decide to have Build branded as a traitor and fired from Tōto's forces to let him act freely. The crime? Sento borrowed a dollark from the Prime Minister and never returned it. Even Banjō can't believe how silly the whole thing is, after he and Kazumi are sent to Build's location under the pretense of getting a single buck back.
  • Five-Man Band: Nascita/Team Build develops into one before episode 13, where they become a Four-Man Band. Later, Kazumi joins the group and they become a Five-Man Band again:
    • The Leader (and The Hero): Sento Kiryū/Kamen Rider Build acts as the de facto leader of Team Build and the protagonist of the show. He plans most of the group’s activities and acts as their primary combatant in the field as Build, while the other characters provide support through their various talents. Emotionally he acts as the core of the group, providing a strong moral center and source of advice to the less experienced Banjō, while the others keep Sento's eccentric side in check.
    • The Lancer: The position initially belongs to Sōichi Isurugi before passing to Ryūga Banjō after Sōichi’s departure. Sōichi acts as an older parental figure to everyone, especially Sento and Misora, providing Sento with his counsel and being the one who first encouraged him to become Build, while Banjō matures into the role after tempering his early selfishness.
    • The Big Guy: Ryūga Banjō/Kamen Rider Cross-Z becomes the muscle of the group, as the only one outside of Sento that can fight as a Kamen Rider, with his hotheaded and impulsive attitude clashing with Sento's cool and collected nature. Each also pushes back against the other's self-loathing tendencies, providing each other with emotional support in times of crisis. Later, Kazumi Sawatari/Kamen Rider Grease fills this role. He doesn't have Sento's genius and equipment or Ryūga's ever-escalating natural Hazard Level, but he's still a good fighter in his own right.
    • The Smart Guy: Sawa Takigawa acts as the master of espionage and information gathering, particularly once she drops her early reporter guise and becomes willing to use her full abilities and connections with Nanba Heavy Industries Ltd. to fight back against them. She's also enough of an Action Girl to save both Sento and Ryūga when all hope is otherwise lost, or at least help them escape.
    • The Chick: Misora Isurugi begins as a cold Deadpan Snarker in contrast to Sento and her father's antics, but over time she warms up to the rest of nascita and becomes supportive and positive in her own way, playing the role of sister to Sento and providing Banjō with an abundance of Ship Tease. She also provides them with support through her status as the idol Mii-tan, whose legion of devoted fans provide her with considerable versatility when it comes to gathering information on Smash attacks, raising funds, or seeking out obscure services.
    • The Sixth Ranger: Gentoku Himuro/Kamen Rider Rogue joins the heroes after a Heel–Face Turn. His immense guilt over what he's done under the influence of the Pandora Box, along with the heroes' reluctance to trust/forgive him prevents him from being an effective ally at first. He does eventually find his resolve to atone for his sins, and the heroes manage to warm up to him (especially since he turns out to be just as prone to silly antics as everyone else), giving the heroes a fourth fighter to add to their ranks.
  • For Want of a Nail: Merging the World of Build with another world, implied to be the main Rider timeline, creates an alternate timeline where Evolt and the Pandora Box never existed, at least as far as Earth is concerned, with only Sento and Banjō remembering the original universe. Gentoku's father is the Prime Minister of Japan and he's his loyal chief aid, Yoshiko Tajimi and Masakuni Midō are part of the cabinet, Nanba Heavy Industries Ltd. never became a Mega-Corp instead being a simple factory, Misora lived a normal life with her father, Kazumi is happy with his friends and still falls in love at first sight with Misora, Banjō was born normally without Evolt's influence and is a successful MMA fighter with his girlfriend by his side, Sawa is a successful reporter with Central Political News on good terms with Gentoku, Sōichi was never possessed and runs his cafe in peace, and Tarō Satō and his band are successful.
  • Gone Horribly Wrong: Project Prominence was meant to bring hope for the future of mankind, but after the Pandora Box created the Skywalls, it only managed to fracture Japan and potentially lead to The End of the World as We Know It.
  • Gotta Catch 'Em All: When all 60 of the Fullbottles, paired as their Best Matches, are inserted to the various panels of the Pandora Box, something "crazy" is supposed to happen. Which is one way to describe it.
  • Hate Plague: The opening of the Pandora Box released some kind of energy that permanently raised the aggression levels of the country's leaders present at the event living, making cooperation in the face of the Skywalls dividing the nation impossible.
  • Heads-Up Display: To make it clear that the rider forms are suits of armor, we occasionally get to see Iron Man style face shots of the people inside the suits, similar to Kamen Rider Birth.
  • Hero with Bad Publicity: Being labeled a fugitive does Build no favors. In episode 3, a couple of bystanders assume that Build is attacking some Smash targets instead of defending them.
  • Hidden in Plain Sight: In Episode 33, Sento searches for information on the Evol-Driver, but finds nothing. However, instead of the standard error message, the computer displays "Nobody knows". So he uses "Nobody knows" as a password when accessing Shinobu Katsuragi's files on Banjō and gets the information he wanted.
  • Hit So Hard, the Calendar Felt It: According to a Freeze-Frame Bonus in episode 33, following the Skywall disaster, the calendar was reset. The year the Skywall disaster took place is ASW 1, where ASW is presumably "After Skywalls".
  • Hostage For Macguffin: Happens quite often, but the heroes more often than not choose 'Macguffin' rather than the hostage, due to realizing more is at stake than a few people's lives, or only pretend to go for it to lay a trap.
  • Idiosyncratic Episode Naming: Or more like numbering. So far all the episode numbers were shown with an equation first then their solution as the episode's number. Doubles as Freeze-Frame Bonus.
  • I Should Write a Book About This: Sento writes a TV series script based on his memories of the events at the end.
  • Kick the Dog: Faust does this as early as episode 2. After Ryūga escapes them, siccing a Smash on him could be considered a reasonable response. But they go the extra mile and turn his fiancée into that Smash, seemingly with the full knowledge that she couldn't handle the process and therefore would force him and/or Build to either leave her a monster or Mercy Kill her.
  • Laser-Guided Amnesia: One debilitating side effect of Nebula Gas exposure is short-term memory loss, which Faust often uses to cover their tracks. They rely on it a bit too much, however, which becomes a liability when one subject's amnesia proves to be temporary.
  • Late-Arrival Spoiler: The second opening showcases two major reveals regarding the identities of important characters.
  • Leaking Can of Evil:
    • All the horrible things let loose when the Pandora Box was opened? It's not open all the way yet. It takes 60 Fullbottles to truly do that, that's simply only what a partially open Pandora Box does. If it's opened all the way, its doomsday.
    • When the first Mars rover arrived on Mars and returned, a piece of Evolt managed to escape back to Earth with it.
  • Leaning on the Fourth Wall: At the end of the series, Sento reveals to Banjō that he plans on sharing their story, having written their experience into a script... 49 episodes long, in fact. He then pulls out a pocket recorder and starts narrating, only for him and Banjō to end up squabbling over the details, exactly as they did in all the previous episode recaps. It's also the exact same argument they had in the first episode recap.
  • Lensman Arms Race: Like its predecessor series, Build moves at a lightning pace with its upgrades, but does so in a much more horrifying context. Blood Stalk manipulates characters on all sides to take more and more dangerous risks with their minds and bodies for an advantage over their opponents that's ever more fleeting, all while seemingly unconcerned with his own place on the power scale. Then one looks at the planet where the Pandora Box used to reside, sees it's a lifeless wasteland, and wonders if all of these powerups are actually worth it.
  • Linear Warriors, Quadratic Wizards: The Transteam Gun users start with much higher Hazard Levels and stronger abilities than the Build Driver users, but the Transteam Gun forces the user to stay locked at that fixed level, which makes it useless in the long term except to deliberately serve as a Starter Villain. Blood Stalk manages to subvert the normal limitations of the system owing to his already being on top of the heap and using the suit as a Power Limiter.
    • The Sclash Driver. In comparison to the Build Driver, Riders that use the Sclash Driver start much more powerful than even experienced Build Driver users. As the series goes on the Riders that use the Build Driver gain more and more modifications that drastically improve their performance while the more rigid Sclash Driver can only grow slowly with the users’ Hazard Level. By the latter part of the series, the remaining Sclash Driver users have to resort to increasingly drastic and dangerous measures just to have a chance of remaining relevant while their Build Driver using teammates have long surpassed them. In the end, the strongest forms of all four heroic Riders use modded Build Drivers.
  • Meaningful Name: Nanba Heavy Industries Ltd., Faust's financial backer. The "nan" in Nanba can mean "south", the one compass direction left out of the three regions, and Nanba is a Mega-Corp powerful enough to be its own faction, becoming one in full when it devours Seito outright.
  • Mecha-Mooks: All of the factions, including Faust, make use of the Guardian humanoid robots to supplement or replace their human troops. This is because they're manufactured by Nanba Heavy Industries Ltd., which had war profiteering as one of their prime motivations for helping start a Civil War in the first place and thus will gladly provide them to all sides. Nanba also has the vastly more powerful Hard Guardians, which they keep for their own exclusive use.
  • Mock Guffin: All sides want the apparent infinite energy source inside the Pandora Box, something Blood Stalk is all too happy to perpetuate the belief in. The infinite energy source doesn't exist. It's all a trap to make whatever poor civilization finds it doom themselves by opening it and activating the Pandora Tower.
  • The Mole: In Episode 26 Kazumi says that one of the core cast is this, since Gentoku was able to steal the Pandora Box despite only Sento, Banjō, Misora and himself knowing where it was. It turns out to be Sawa, who's one of the "Nanba Children" and had hidden a listening device in Ryūga's Dragon Fullbottle. However, it's then subverted when it's revealed that Sawa is still a good guy and she only spied on the group because Nanba is holding the Nabeshima family hostage again. Plus, the bug was actually planted by someone else.
  • Mood Whiplash: The story sure has some abrupt transitions between silly and horrifying. Face doodling and memories of being experimented on in span of five minutes, folks.
    • The Previously On segments are another source of this, since even the show's villains will participate and act goofy during them.
    • Episode 30 starts with the main cast acting like children in front of Mars' Queen Vernarge, then recapping what they know with a puppet show that teasingly references the long-standing Ho Yay between Sento and Banjō. It ends with Sawa telling Misora that Banjō might not even be human.
  • Mugged for Disguise: Ryūga gets to pull this off in episode 10, greatly expanding his options.
  • Mundane Solution: Apparently motorboats are all that's needed to find and slip through gaps in the Skywalls (you need a special pass to travel legally, though), and wireless signals can go right through if the three state leaders can still teleconference every month. Underground tunnels also weren't affected, and weapons of sufficient force can just blow a hole in the thing. It's eventually made explicit that the physical barriers formed by the Skywalls aren't actually what's keeping the country divided, but rather the insanity and lust for power that the Pandora Box inflicted on Japan's leaders, and the Skywalls are just there to be an excuse to stay divided and act as a source of Nebula Gas.
  • Nebulous Evil Organisation: Faust, the organization that are responsible for the Smash. Night Rogue and Blood Stalk are Faust's high-ranked members. They're actually an unsanctioned military project run by a leading member of Tōto's government, and nearly every named character at the Tōto Institute of Advanced Matter Physics is actually a member of Faust.
  • Not Himself: The energy released when the Pandora Box was opened in 2007 distorted the personalities of everyone present, making them aggressive and warlike, which is a major reason why the three nations haven't tried to reunite in the intervening decade. Tōto's Prime Minister Himuro was unable to attend the ceremony, which is why he remains a Reasonable Authority Figure. When those affected are returned to normal, they tend to suffer My God, What Have I Done? moments because they remember everything they did while under the Box's influence.
  • Once-Green Mars: Implied; the Pandora Box was found in ruins on Mars implying a civilization once thrived there. This is later confirmed, and it was the Pandora Box was what destroyed it thanks to a singularity appearing over the Pandora Tower that sucked up everything on the surface.
  • Once More, with Clarity!: The incident where Ryūga was framed for murder is revisited several times throughout the show, each time providing more clarity about who was there, what they were doing, and why. Episodes 27 and 28 pull off a smaller example with a conversation between Sawa and Sento.
  • Only the Chosen May Wield: In episode 6, Ryuga attempted to use the Build Driver on himself to transform and use against Sento, ignoring Sento's warnings. When the Build halves go onto him, the process rejects Ryuga painfully. Sento takes his Build Driver back, saying it's not something any amateur can do so easily.
  • Phlebotinum-Handling Requirements: Not everyone can use the Build Driver, one needs a Hazard Level of 3 or more. If anyone else tries to use it, they're painfully electrocuted, as Ryūga Banjō finds out the hard way. It takes Level 4 to use a Sclash Driver, and Level 5 to properly use the Evol-Driver. Attempting to use either of these drivers with insufficient Hazard Levels only leads to increasingly painful and potentially life threatening rejection.
  • Power Levels: "Hazard Level" is the measure of a subject's resistance to the effects of Nebula Gas, and accordingly how much of its power they can draw out.
    • Level 1 is the minimum. It indicates a subject who will transform into a mindless Smash upon exposure to Nebula Gas, but will die shortly after their essence is extracted. The only example of someone at this Hazard Level in the series, Kasumi Ogura, was terminally ill prior to experimentation.
    • Level 2 is the typical level of a healthy human. These subjects will also become mindless Smash upon exposure to the gas, but can survive essence extraction without long-term effects beyond a brief period of short term memory loss. Any level higher than 2.0 allows the subject to maintain their human form rather than become a Smash and control themselves in Smash form. Subjects from this level onwards begin to exhibit enhanced physical abilities in their human form that increase with their Hazard Level.
    • Starting from Level 3, subjects can transform into a Kamen Rider. Level 3 is the bare minimum needed to use the Build Driver.
    • Level 4 is the minimum for the Sclash Driver, albeit with a side effect of increased aggression and potential loss of inhibition until their Hazard Level grows sufficiently to handle the concentration of Nebula Gel compared to Nebula Gas.
    • Level 5 is supposedly the maximum a human subject can withstand safely. It's impossible for normal humans to reach this Hazard Level without heavy modifications. It's also the minimum required to use the Evol-Driver.
    • Level 6 pushes the subject beyond their human limits, which would normally prove fatal if not handled properly. Sento first achieved this by inserting a panel of the Pandora Box into the Build Driver, intending for the power overload to kill both him and Evolt. Said Panel was later used by Katsuragi Takumi to create the Genius Bottle, which allows him to reach such levels safely.
    • Level 7 is the point where the subject gains abilities that supposedly defy the normal laws of physics, but is impossible for a human to survive barring unique cases of heavy modification. The upgrade to this level also affects the Fullbottle that is most compatible with the subject, upgrading it to a new form. Two such bottles can be used as a Best Match, ignoring even the Organic-Inorganic rule.
    • Even when using a lesser Driver, higher Hazard Levels improve the strength of the user's Rider form: for instance, a Level 3.2 Vortex Finish does nothing to harm Blood Stalk, while the same attack at Level 3.7 successfully injures him. Methods of increasing one's own Hazard Level include battle, intense anger and various kinds of Deadly Upgrade such as repeated Nebula Gas infusions and the Hazard Trigger.
  • Pretext for War: It becomes apparent Tōto is the only one of the three groups formed from the fractured Japan to actually want peace, and the other two are looking for any excuse to start an all out war. Justified, as Tōto was the only faction whose leader isn't corrupted by the Pandora Box's Hate Plague. Night Rogue decides to give them a reason by stealing the Pandora Box from the institute where it's kept under lock and key and only accessible by all three leaders at once.
  • Previously On: Done by the characters, as if to contribute further to the Mood Whiplash.
  • Primary-Color Champion: Build's default RabbitTank form is half-red (from the Rabbit Fullbottle) and half-blue (the Tank), with a decent amount of black from the undersuit, admittedly.
  • Public Domain Artifact: A cube found during an Mars expedition was called the Pandora Box after being opened it released the "Skywalls", kickstarting the series. (Now, it’s not actually the basis for the one in Greek Mythology, or at least it hasn’t been said to be yet; it’s just the logical name for the box you open and cause all hell to break loose.)
  • Psycho Serum: Nebula Gas. Exposure transforms you into a powerful monster... who's completely insane and a rampaging beast. The purification that creates Fullbottles purges this effect. Unfortunately, turning an essence from the liquid form into the solid jelly form, creating Sclashjellies, turns it back into a Psycho Serum that increases the user's aggression with each use. The Hazard Trigger does the same thing to an even larger extent with the basic Fullbottles by overclocking them to insanely high levels. The FullFull RabbitTank Bottle has to be explicitly made to negate this effect.
  • Reality Ensues:
    • The entire country being split into three pieces in a cataclysmic event is treated as a gigantic disaster, and the fact one of the three countries is devoted to economic recovery shows it had more impact than just geological.
    • While travel between the countries is possible, travel between mainland Japan without going around the Skywalls isn't. There are small openings in the Skywalls, but they're few and far between and too small to be reliable means of trade or moving between the separate sections. This combined with the Hate Plague the Pandora Box unleashed ultimately lead to the three divided areas growing away from each other and unable to recover from the disaster until they've become separate countries.
    • The whole mess with the Skywalls has weakened Japan to the point other countries are trying to annex them.
    • Hokuto's soil was altered by the Skywalls and their crops were completely devastated. This caused an economic collapse and people are extremely desperate to escape to the other countries due to the resulting famine.
    • Criminal organizations don't just get money from nowhere. Faust gets its funding from Nanba Heavy Industries Ltd., which also gives them a bit of blackmail material to use to manipulate the organization.
    • The Guardians are cannon fodder to the heroes, who even without their suits are superhuman, but they're still heavily armed robots much stronger than a baseline human. When pitted against normal human soldiers, it doesn't go well for the humans.
    • The Riders can deal with the Smash on their own, and pretty much mow down any lesser variety after a certain point. When put into a military context and pitted against normal humans, they're dangerous Super Soldiers.
    • Even after the representative battle between Tōto and Seito ends in Tōto's victory, Nanba reports that Seito won anyway so he can continue the war.
    • Even though Evolt at his peak is powerful enough to create black holes that can devour entire planets to use as energy, it still takes a tremendous amount of energy to travel between planets on his own, thus losing most of the energy he just gained. The main reason he needs the Black Panel of the Pandora Box is to create wormholes so he doesn't waste energy and remove the chance he would be stuck in another situation like Mars.
    • Evolt's species lost both their strongest member and their ultimate weapon millions of years ago. Come the present when Evolt regains contact, only three of them are still around. A hyper aggressive race losing their two strongest weapons in one swoop will result in its decline.
  • Recursive Canon: With the world reset such that none of the tragedies of the last ten years ever happened, Sento and Banjō are the only ones who remember the world as it was. To help deal with this, Sento writes his memories down as... a set of scripts for a 49-episode TV series. The series ends with Sento and Banjō performing the Opening Narration of the second episode together, as "Kamen Rider Build is a work of fiction" appears on the screen. It is very likely that the Opening Narration we've seen in every episode is actually Sento and Banjō from after the finale.
  • Remember the New Guy?: The villains in Kamen Rider Build Be The One claim to have been on Earth since the Skywall Disaster and subtly manipulated events to their own ends; a few flashbacks show them working as assistants to the leaders of the three nations, and in particular Mitsuomi Gōbara, the Zebra Lost Smash, says that it was his idea to turn Ryuga's girlfriend Kasumi into a Smash, and Kengo Inō/Kamen Rider Blood takes credit for mindwiping Takumi Katsuragi, creating the Sento Kiryū persona, and manipulating him to serve their own ends.
  • Revisiting the Roots:
    • According to Word of God, the series is intended to do this. The most obvious case is the return of some Shōwa Era conventions like the monsters being created through experimentation by an evil organization, but other older Rider formulas can be seen, such as the parallels to Kamen Rider Double, and there being only one Rider until later when a single secondary Rider appears with only one base form and no gimmicks.
    • Something that's not noticeable at first is the return of the Rider Kick as the primary finisher when past Heisei Era Kamen Riders rarely uses it.
  • Robot Buddy: Cross-Z Dragon, a robotic dragon that turns into Cross-Z's Build Driver add-on. With the FullFull RabbitTank Bottle, Build gets either a robotic rabbit or a squad of tanks that become armor for RabbitRabbit or TankTank Form. The Cross-Z Dragon becomes the Great Cross-Z Dragon once Ryūga gains his Great Cross-Z form. In Kamen Rider Cross-Z, Kamen Rider Kilvas has the Kilvaspider which functions in the same way as the Cross-Z Dragon.
  • Rule of Symbolism: Thanks to video footage somehow pulled from the Pandora Box itself, it's revealed that whatever destroyed the civilization on Mars first came out of the Pandora Box and took the form of a tower, which Blood Stalk is starting to rebuild. The allusion to the Tower of Babel is fairly obvious.
  • Science Hero: "Science" is the big theme the way the last few Riders were themed around video games, ghosts, cars, fruits and even gemstones. His Rider Kick even summons and follows a line graph.
  • Sealed Evil in a Can:
    • The series is kicked off by the Pandora Box being opened and releasing the Skywalls and dividing Japan into three separate countries. It also released a Hate Plague on those in close proximity and the Skywalls emit Nebula Gas, which is used to turn people into Smash. Worse yet, the walls are merely the incomplete pieces of the Pandora Tower. If the tower is completed, it will mean the destruction of humanity.
    • It also contained an evil spirit (namely Evolt) that possessed Sōichi that'd been stranded on Mars for millions of years when he picked it up and now seeks to destroy life on Earth.
  • Set Bonus: Some of Build's Fullbottle combinations make the Build Driver declare "Best Match"; it's not clear what makes the Fullbottles so compatible, but the resulting form is more powerful than non-Match ones. Each Fullbottle has a label on the cap that helps indicate its Best Match combo (for instance, Rabbit and Tank have "R/T" labels). Playing around with the Build Driver toy revealed that it's pre-programmed with sounds for 32 Best Matches total, not counting promotional or Legend Rider items.
  • Shoo Out the Clowns: A variant. The usual comedic Previously On recap is cut out in Episode 29, instead showing the devastation of both Nanba unleashing the Hard Guardians, and Blood Stalk beginning to build the Pandora Tower.
  • Significant Anagram: nascita is an anagram for satanic. Its owner is a rather satanic figure.
  • Small Role, Big Impact: Had it not for Tarō Satō visiting in an inopportune moment, Sento Kiryū wouldn't have been given his face.
  • So Last Season: Averted, surprisingly, by Rogue and Stalk. Unlike true Riders, their Hazard Levels are unchangeable, meaning they should fall behind as the Lensman Arms Race continues, right? Well, Rogue switches over to proper Rider gear after a certain point, and Stalk has a habit of pulling I Am Not Left-Handed. He needs the Riders’ power to increase, and doesn’t actually want to kill them, so he’s not using his full strength. Every time he needs to stop someone who seemed equal or stronger to him last time, he pulls out a new power to shut them down quick. His power can’t increase but in truth it’s a lot higher than RabbitTank Sparkling’s debut made it look. As everyone continues to upgrade, he continues to keep up despite being the only one with nothing but his original default suit. And then he gets his upgrade, and it's better than everyone else's combined.
  • Spanner in the Works: The Skywalls themselves are eventually revealed to actually be this: Evolt's original plan was just to touch the Box and wipe out the Earth right then and there. Because some of the Fullbottles within the Pandora Box got empty during the long amount of time the Box was sitting on Mars, it didn't have the power to destroy the Earth and simply created the Skywalls instead.
  • Spell My Name with an "S":
    • The toy catalog labels the Ninja Fullbottle as "Ninjya". Unlike most of Toei's odd Romanizations, is apparently a legitimate (if uncommon) way to spell the word in Japan.
    • One magazine scan got its Ls and Rs mixed up, labeling a suit "GolliraMond Form".
    • As per usual, official English spelling of characters' names tended to differ from what the fanbase guessed they were. Night Rogue was originally thought to be Knight Rogue or Nitrogue, among other things; while Blood Stalk was thought to be Blood Stark. Ryūga's Rider name was first thought to be "Close" based on pronunciation, then most people adopted "Claws" as it matched his dragon theme. Even when evidence emerged that it was "Cross", nobody expected it to have Xtreme Kool Letterz and be "Cross-Z".
    • "KaizokuRessya" Form and its "Kaizoku Hassyar". More accurate romanizations would be KaizokuRessha and Kaizoku Hasher.
    • "Evolt" vs. "Evolto". Episode 33 showed the name spelled out in English text onscreen, revealing it was "Evolto", but official merch for Kamen Rider Build Be The One also shows it as "Evolt".
    • A minor one exists in the name of the Disc-One Final Boss due to the way Japanese writing works. Is his name "Jūzaburō Nanba" or "Juzaburo Namba"?
  • Spoiler: Played for Laughs in the Previously On segment of Episode 30, which has Jusaburo Nanba as Prime Minister Midou praising Nanba Heavy Industries Ltd.. Sento suspects something is up and starts asking questions, but "Midou" replies "You can't just go revealing spoilers like that in the recap!"
  • Spoiler Opening: The opening of Build shows countless advanced scientific breaking through and destroying the Skywalls as Build looks on. The finale features the very same thing occurring, except with The Reveal that it was Build himself who was causing that very event in order to create a new world without the Skywalls ever happening in the first place.
  • Story Arc: The series is divided into story arcs similar to Kamen Rider Gaim and Kamen Rider Ex-Aid. In order:note 
    • "Birth Arc (1-16): The first arc is mostly focus Sento and co.'s effort to uncover the truth of the mysterious "Faust" organization. It also focuses on Sento trying to recover his memory and Ryūga trying to clear his name.
    • "War Arc" (17-28): This arc focuses on the Civil war between Tōto, Hokuto and Seito and it's toll on the main characters
    • "Evolt Arc" (29-49): In the final arc, the true mastermind of all the chaos that hit Japan is finally revealed to be Evolt, a mysterious extra-terrestrial being and the one who destroyed the Martian civilization. Sento and co. must join forces with former enemies in order to defeat Evolt, uncovering some startling truth about the people close to them in the process.
  • Suicide Mission: The Riders all somberly accept that entering the Pandora Tower to finish off the ludicrously powerful Evolt in the place he has a Home Field Advantage is one of these, but if they don't everyone in the universe will be consumed by him. Sure enough, Grease and Rogue both die in the process, but the group ultimately succeeds in destroying Evolt once and for all and creating a Merged Reality were he never existed.
  • Super-Fun Happy Thing of Doom: Each of Japan's new regions is seemingly devoted to benign and benevolent ideals and social practices. All three are also effectively at war with one another for the Pandora Box and keep tight grips on the citizenry under their respective controls.
  • Sword of Plot Advancement: The Hazard Trigger fills this role. Introduced in episode 19 as an extremely powerful but extremely dangerous weapon, the next two major story arcs are dedicated to Sento's attempts to master it, and it becomes vitally important in the endgame as a key to stopping the Big Bad in several different ways.
  • Talking Is a Free Action: Averted repeatedly.
    • After Banjō figures out that the Dragon Fullbottle enhances his punches, he pauses to admire it and claim that the fight will be easy... only to find that the Guardians have surrounded him while he was distracted.
    • During the representative battle between Build and Rogue, they get into debate about the purpose of the Rider System and whether Sento is still the Devil's Scientist. Rogue takes advantage of the lull in the fight to ready a Funky Shot from the Nebulasteam Rifle.
    • MadRogue copies the above trick by charging up the Kaizoku Hassyar in the middle of a Hannibal Lecture.
    • After Evol finds himself overpowered by Build's Genius form, he decides to stop playing around and use Black Hole form only for Build to grab the Evol-Trigger and finish him off before he gets the chance to transform. Tellingly, Evol shows up to their next encounter already in Black Hole form.
  • There Are No Therapists: None of the government leaders have been investigated for their mental stability in the wake of the Skywall event. If anything, the whole thing about them being affected mentally is an open secret.
  • This Is Reality: In Episode 39, Katsuragi dismisses Misora's belief in The Power of Friendship by saying "This isn't a Shōnen manga."
  • Tomato in the Mirror: Talking with Ryūga about the similar experiments that were done on them makes Sento realize that their purpose was to create Smash, the very foes he fights against.
  • Villain Song: "Evolution" for Evol's debut.
  • Vitriolic Best Buds: Sento and Ryūga in spades. The only scenes they share where they aren't bickering and making constant digs at each other are the dramatic ones. They even bicker in the Opening Narration!
  • Walking Spoiler: Pretty much everyone, once things start to get complicated.
  • The Wall Around the World: The Skywalls, unleashed by the Pandora Box, split Japan into three parts. Downplayed example, since the barrier stretches only from the center of Japan and fades into the sea before reaching any other country. They're actually for a much more sinister purpose: they're components of the Pandora Tower, and if the tower is completed, its The End of the World as We Know It.
  • War Arc: As of episode 16 one has started when all out war between Tōto and Hokuto begins with the heroes caught right in the middle.
  • War for Fun and Profit: Night Rogue and Nanba both seek to start an all out war between the three groups, but for different reasons. In Night Rogue's case, it's so Tōto can come out on top of what he sees as an inevitable war, and in Nanba's case, he's simply a good old fashion war profiteer seeking to make money off of the resulting weapons deals.
  • Was It All a Lie?: Asked verbatim in Episode 14 by Sento to Sōichi. The latter responds "Not ALL of it", admitting that there were times when Sento and Ryūga legitimately surprised him and when he felt bad about betraying them. However, Sento dismisses this as a bad joke.
  • Was Once a Man: As part of this series' call backs to older Rider series (especially classic Shōwa Era style Riders) the Monsters of the Week, the Smash, were normal humans who were experimented on and turned into monsters. However, they're turned back to normal instead of killed similar to the Dopants or Zodiarts unless some terminal illness or debilitating condition still affects the human, in which case they're Killed Off for Real, but it's better than remaining a mindlessly destructive beast.
  • Wham Episode: Much like the previous series, episode 10 kicks off a long chain of them as the entire premise of the show up to that point begins to unravel.
  • When It All Began: The Skywall disaster ten years ago, which divided Japan into three regions.
  • World of Snark: Despite the Darker and Edgier premise, the show actually derives a lot of humor with quips from nearly every named character.
  • World-Healing Wave: In the finale, Sento's final attack on Evolt erases him from history, creating a world that never suffered under his schemes.
  • World-Wrecking Wave: The Pandora Box being opened unleashed a localized one for Japan. The Skywalls violently erupted from the ground across the country, causing property damage and throwing any poor person too close to them hundreds of feet into the air, a Hate Plague was unleashed on those in close proximity, Hokuto's portion of the country had its soil altered such that a famine resulted, and Nebula Gas is being constantly emitted by the Skywalls, which can mutate people into horrible monsters. From the video footage gained from Misora's bangle in episode 25, it looks like opening the Pandora Box completely will result in an exponentially more powerful surge ripping through not just Japan, but the rest of Earth. Just look at what happened to Mars...
    • #36 makes it clear that it's something far worse. The box doesn't just unleash a wave of destruction, it opens a Black Hole to strip the planet of everything.

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