A commenter on the JEFusion page for the Kamen Rider Build toy preview stated that the DrillCrusher fits thematically with Build's RabbitTank form, since the drill part looks like a Carrot and the Cannon form works like a tank's cannon.
At the first glare, Fullbottle combos that make up Best Matches might look random and as revealed in episode 41, the Inorganic Bottles side actually are mostly random, but there are actually some connections between them:
RabbitTank: Both have something to do with movement: A rabbit is usually associated with jumping and hopping, while tanks were created to support infantry movement.
GorillaMond (Gorilla + Diamond): Both of them are associated with strength. A gorilla is mostly associated with power and brute strength, and is even prominent in many animal-themed Riders and Sentai series as component of a power-based form, while diamond is obviously one of the strongest and hardest jewels.
The Vortex Finish involves punching a wall of diamond. This is a case of Shown Their Work, for as much as diamonds are renowned for their sturdiness, that only extends to them getting cut. Diamonds are far more vulnerable to blunt force than most people would think.
HawkGatling (Hawk + Gatling Gun):
Both are associated with violence and flight. Hawks are aggressive apex predators and of course can fly, while Gatling guns can fire hundreds of bullets per minute and are used on attack aircraft.
Both are associated with altitude travel. Pandas climb trees to get food, while rocket ships are built for travel high in space.
They're also both Chinese associated.
People also compared this form to Fourze. Fourze is a rocket-themed rider with a panda's color scheme.
Pandas are known to eat bamboo and a certain Lunarian princess is associated with Bamboos, and even has a bamboo rocket AND wears a bamboo space helmet in Ōkami, where she is part of a side quest to return to the moon.
FireHedgehog (Hedgehog + Firetruck): Both are associated with protection; a hedgehog has quills to protect it from predators and a firetruck protects people from fires.
LionCleaner (Lion + Vacuum Cleaner):
Both have to do with cleanliness. Soujiki being a vacuum cleaner should be easy to understand, and lions are known to groom their young.
Also, both are noisy.
Ironically, some cats are scared shitless of vacuum cleaners (though not as much as dogs)
A lion can bite things into smaller pieces for the vacuum to suck in easier.
KeyDragon (Dragon + Lock): Both are associated with treasure protection. A lock is often used to keep a treasure chest shut while dragons are said to guard hordes of treasure.
Both are also often associated with Japanese RPG games set in a High Fantasy setting, which helps explains why with the word "key" included, the form is called the "Seal of Fantasy Star". This is also likely why "lock" is changed to "key".
KaizokuRessya (Pirate + Train): Both are associated with transporting goods and use of revolutionary transportation to travel.
They also both have Super Sentai teams associated with them.
OctopusLight (Octopus + Light Bulb): Both have to do with light through non-solar means. The lightbulb does so through electricity, while the octopus does so through bioluminescence.
Or maybe a foreshadowing of Sawa getting turned into an octopus-like Smash, with lightbulb representing camera's flash used by reporters.
As seen by the form's finisher move in Episodes 13 and 14, both can also be associated with temporary blinding. Octopus can blind its enemies using ink, while too much flashes of lights from lightbulbs can also blind you.
PhoenixRobo (Phoenix + Robot): Both are considered immortal in different ways; a phoenix is reborn after death each time, while robots can always have their memories and programming saved and uploaded to a new body, even if their own does rust, meaning there can always be a new one.
Both can be either alone or together, with smartphones causing both isolation and being able to socialize with others, while wolves are either loners or travel in packs.
Both are also able to communicate over long distances, wolves by howling and smartphones by being...well, smartphones.
Or it could just be a Kamen Rider Faiz reference, especially considering how the combination and the Build Driver itself was designed by a man named TAKUMI Katsuragi.
UniRaser (Unicorn + Eraser) : Unicorns are often said to have magic powers, like magicians. One of the most famous magic tricks performed by magicians is dissapearing things, just like the Keshigomu Full Bottle when used in the Sclash Driver.
A popular belief is that a unicorn's horn can remove contamination from water, just as an eraser removes marks from paper.
Some people believe that unicorns were real until they went extinct, or in other words, were erased from existence.
RoseCopter: Both use the air for transport. Roses, for their pollen, and petals, helicopters for ferrying people.
It could be a subtle reference to Guns N' Roses. A helicopter rotor rotates on a fixed Axle.
TurtleWatch: Both have to do with time. A watch can tell time, and turtles live for a very long time.
BeetleCamera (Rhinoceros Beetle + Camera): What are tiny cameras called again? Bugs.
Additionally, both use compound lenses for their optics.
Perhaps even a reference towards Sawa's identity as a fake reporter spy, who did bug the Nascita base.
KumaTelevi (Bear + Television): Perhaps a reference to Persona 4.
Since this is the Hyper Battle DVD form, it looks like it's a reference to Televi-Kun, the magazine which is often involved in the Hyper Battle DVDs. Reverse the word order for this form, and you get "Televi-Kuma".
Before and during hybernation, bear and other animals tend to get fatter and not move a lot. Watching TV is also linked to sedentarism, making people fatter and not move a lot.
DogMic (Dog + Microphone): Both involve increasing a sound's volume. Dogs are known for having much better sense of hearing than humans, while a microphone makes sounds louder.
It also brings to mind a dog barking.
MerryChristmas (Santa Claus + Cake): Both have to do with Christmas. Santa Claus delivers presents to children at Christmas, and cake, specifically Japanese Strawberry Shortcake, is the Japanese equivalent of Christmas Cake.
SpiderCooler (Spider + Refrigerator): Spiders wrap up their prey to consume later while refrigerators and coolers are used to keep food cool so you can eat them later.
ToraUFO (Tiger + UFO): Both attack unseen, tigers when they ambush their prey and UFOs when they abduct people. Or they both could go forcattle.
KujiraJet (Whale + Jet): Ever hear of a jumbo jet? Not only is it big like a whale, it also sort of looks like one.
ShikaMid (Deer + Pyramid): Both are associated with guarding something. A deer is sometimes portrayed as a forest guardian, while a pyramid (in theory; in practice, not so much) guards the Pharaoh resting inside from thieves.
It could also be a reference to the Ino-Shika-Cho combo in the card game Koi-Koi and stacking cards into a pyramid is a common party trick or you can play pyramid solitaire.
KirinCyclone (Giraffe + Fan): Giraffe's are known for their long necks while many fans have long stands.
PenguinSkater (Penguin + Skateboard):
Both can slide along a surface. A penguin can slide on ice/snow using its belly, while a skateboard basically slides along the ground.
Also, remove the wheels from a skateboard, and you have the kind of skateboard people used on snow.
Some people ride skateboards on their bellies periodically, in a manner reminiscent of a penguin.
BatEngine: Both have to do with vibrations. Bats use vibrations in the form of echolocation, and engines vibrate when they are running.
HachiMarine (Wasp + Submarine): Both are known for assaults. Wasps assault aggressors by stinging them and submarines assault enemies from underneath.
SaiDryer (Rhinoceros + Hairdryer): Rhinos' horns are made from the same material as human hair (keratin), which is what hairdryers are used to, well, dry.
GoldScorpion (Scorpion + Gold): Both are often found in Egypt and other deserts. Scorpions live in deserts as a habitat, and gold is hidden in ancient tombs, usually thought of as being located in the desert.
CrocodiCon (Crocodile + Remote Control): Both have to do with how certain actions can be triggered by certain impulses. Crocodiles can easily get upset if someone approaches a mother croc who is guarding her eggs, and remote controls can trigger actions with a simple impulse, usually the press of a button.
F1Saurus (Dinosaur + F1): Cars use fossil fuels, and dinosaurs leave behind fossils.
CupEnergy (Cup Noodles + Energy Drink): Both are victuals (food and drink) that give the consumer energy over a period of time. Cup Ramen contains noodles, which are a source of carbohydrates, thus they give the consumer energy over a long period of time, and energy drinks, specifically Japanese energy drinks, have a lot of caffeine in them that keep the consumer awake.
Super Hero Time (Super Sentai + Kamen Rider): Both air in the one-hour long programme block on the Japanese television network, TV Asahi, which air the new weekly episodes of the Super Sentai and Kamen Rider series.
ButtobaGanba (Kamen Rider Buttobasoul + Kamen Rider Battle: Ganbarizing): Both are Kamen Rider-based arcade games.
There is also a reason why some of the Fullbottles above are considered organic or inorganic despite their weird motifs.
Why would a ghost be considered organic? Unlike the other creatures from mythology and folklore featured as Fullbottles, ghosts are said to have no physical form. However, in pseudoscience of 19th and early 20th century, ectoplasm is a substance claimed by mediums to have come from ghosts.
Super Sentai is organic, because most Super Sentai are normal humans that can transform into rangers.
Kamen Rider is inorganic, because Kamen Riders are known to be Cyborgs or other types of modified humans.
Energy Drink is inorganic, because those drinks are full of many artificial substances.
The Build Driver design might seem weird at first...until you realize that a more accurate name for the Fullbottles might be the Full Cartridges - when he transforms, he's surrounded by structures similar to Gunpla runners; How are runners made? By injecting plastic into a mold, with the cartridges supplying the mold with the material. In other words, his driver is based on a 3D printer.
Build's symbol is this. The circular part resembles the Yin-Yang symbol, as in two opposing halfs (organic and inorganic) coming together to make a unified whole.
Keep part with the Ying-Yang symbol reference, the two of the colours of Build's main form came from the Korean Taegeuk. When Build is in Sparkling Form, it adds white to the suit. Red, blue, white and black is from the Korean flag.
Build's suit looked a little weird when I saw it. With the color of the mask on the right being on the left hand and vice versa with the left. At first I thought it was because it was to help distinguish from W, but then it hit me. Our brain is cross-wired. Meaning that the right side of the brain controls the left hand and again vice versa, which explains why the suit is like that!
Just a little one for science/math geeks but R/T's finisher is a literal linear equation.
Here's the thing about how the graph works - for every increment in the value in the original equation, the answer will grow lower and lower by decimals without ever actually reaching zero, which is why the line tapers off and runs off horizontally. The theory being that the line will go on forever without touching the value of zero. After two pastKamen Riders have had a final form associated with infinity, it's fun to see a Kamen Rider who's weaponised the concept of infinity.
Ryuuga displays the surprise ability to do all sorts of stuff with his feet in episode 2 - as a professional boxer he's required to be just as dexterous on his feet as he is with his hands, despite the obvious nature of the sport.
Sento and Ryuuga match the Organic/Inorganic formula that makes a Best Match. Sento, as the inventor of the Build Driver and all Build's weapons, is the Inorganic; while Ryuuga, as a former professional boxer who aside from the Dragon Fullbottle has no artificial advantage against his opponents, is the Organic.
Artemisia Dracunculus is a plant, commonly used as a spice tarragon, that was believed to protect from snakes and cure snake bites. Dracunculus can be translated as small dragon. That's exactly what Cross Dragon is. A small dragon that saved Ryuuga from poison of cobra-themed Blood Stalk.
Why make the 'pet' looking after Ryuuga a dragon? Sento had already noted that the Dragon bottle fits with 'ryu' (dragon) in Ryuuga's name, so he decided to grace his jumpy partner with another dragon.
Kishida is depicted as The Chew Toy off the bat, meaning he's required to survive a certain amount of abuse. As of episode 6 he's the first person to come out intact after being turned into a Smash twice in a row, a rare bit of positive fallout while at the same time lending our heroes some hope.
At one point, Sento used NinninTank form. Because he was at a dark place at that time, it is better to capitalize Ninja's stealth with an appropriately colored half Explanation Ninja is purple while Tank is blue. Both are dark colors allowing Build to hide well in the dark. than to go for the Best Match Explanation Comic is bright gold, making Build stand out too much in darker areas.
Ryuuga seems to prefer going after Blood Stalk when he has the choice to fight him or Night Rogue. Sort of ironic when you consider that Blood Stalk is The Dragon.
Episode 8 heavily implies that Souichi's the one responsible for every disguise Ryuuga has been wearing. Considering Souichi himself has been in hiding from both the government after the Pandora's Box incidentand Faustafter rescuing Misora, it's not a huge stretch to assume that he had to use them too.
I just came with this idea, but at least some of the Best Match Full Bottles are not only associated by some similar properties, but also related scientific topics:
RabbitTank: Vertical (Rabbit and its jumping) and Horizontal Movement (Tank)
GorillaMond: Strength of Material, for both destruction (Gorilla) and protection (Diamond)
HawkGatling: 2-D (Gatling) and 3-D (Taka) Movement.
LionCleaner: Air Pressure (Lion's scream let air go out, while Vaccuum Cleaner sucks air in. Both of them rely on controlling/changing air pressure.)
SmaphoWolf: Modern (Smartphone) and Traditional (Wolves with their howling) forms of Communication.
KujiraJet: Archimedes' Buoyancy Principle. One being exerted on by liquid (Kujira) and the other by gas (Jet).
Why do the newer upcoming Riders and Rider upgrade use Sclashjellies instead of Fullbottles? When some liquids are condensed/concentrated they congeal into jelly. The Sclashjellies are Fullbottles that have been purified even further.
And if jelly represents solid, Fullbottles holding liquid, then RabbitTank Sparkling Fulbottle represents gas as a soda can.
Soda's still a liquid. What represents gas is the substance used to create both, Nebula Gas.
Given episode 9, Faust has a way of reproducing the same type of Smash and hence, mass producing Build's Fullbottles for the military.
It may seem strange that the Legend Rider Best Matches for Decade features two inanimate objects (Camera + Card). However, Camera can indeed be used for an Organic slot by seeing it as the Cameraman Fullbottle.
Alternately, it could be seen as the 'Card' bottle might represent Decade's Rider Cards, which contain the essence of living Riders, and beside that a good number of Kamen Riders are organic in nature (as in, their belts mutate the Rider, instead of magic/technology to transform them).
KeyDragon’s Vortex Finish doesn’t seem to have any scientific equations, graphs, or formulas appear. Just a chain and some fire. Make sense though, since dragons are mythical.
The same can also be said to PhoenixRobo's Vortex Finish, as the finisher utilizes more of a Combo Platter Powers of Wreathed in Flames and Flight ability of a phoenix, seemingly without Robot Fullbottle ability being used. Just like dragons, phoenixes are mythical.
Then again, this can't explain why SmaphoWolf's Vortex Finish doesn't seem to have any scientific equations, graphs, or formulas appear. Only spinning application icons to trapping the target(s) and then summon a black wolf silhouette to attack them. All while the wolves are real-life animal.
It can be a reference to the zoetrope, an early animation device that produces the illusion of motion by displaying a sequence of drawings. See how the wolf is running around with afterimages along the icons.
Sawa becoming an octopus-like Smash, octopus is known for it's amazing camouflage in hiding itself, a spy needs to hide his identity well enough. Also her hair curls seem to invoke an octopus and it's tentacles.
Blood Stalk being The Starscream to Faust and betraying the heroes by being Souichi makes a lot of sense, given his snake theme. After all, if someone is a liar or particularly deceptive, you might call them a snake, or "a snake in the grass".
RabbitTank Sparkling's soda bubble effects might seem silly at first, until you realize that they aren't supposed to be soda bubbles, but molecules.
Sento insults Ryuga by calling him an ape. Not only he is fairly creative with it, it is even a scientifically accurate insult. Humans (Homo sapiens) count among apes in zoology.
Also, the only ape species represented by a Fullbottle is the Gorilla. When used, it increases Build's punching power. Now, what is Banjo's main form of combat?
Kamen Rider Grease having the Helicopter Fullbottle makes sense given that helicopters are a form of machinery which is what Grease's theme is.
So why did the Dragon Sclashjelly not work for Sento? Because the Fullbottle that was used to create it was in use more with Cross-Z, and given how Build struggled with KeyDragon in the past, there was no way Sento could handle a more powerful version of Dragon's powers.
Heisei Generation Final is the gathering of the Neo Heisei Riders. A very intriguing tidbit is that Fourze and OOO were connected to Double who started the Neo Heisei Era. Gaim and Ghost were connected to Drive who is between the two, middle. Lastly, we have Ex-Aid and Build who be the last two before the new rider appear in a later date, the End. Therefore, Start, Middle, Finish.
As mentioned in Mythology Gag, the Hokuto Three Crows' names can be a reference to Kamen Rider Kiva aside from being led by a character whose actor also played Otoya Kurenai.
Castle Hard Smash to Castle Doran (fitting with Build's organic-inorganic theme, is a dragon and a castle rolled into one) and both use Breath Weapon. Incidentally, his first on-screen fight was against the dragon-themed Ryuga. Kurenai/crimson is a shade of aka/red. He could also be a reference to Rook/Lion Fangire.
They were all killed eventually. What do you call a group of crows? A murder.
References to Otoya Kurenai's enmity with the Fangire in the fight in Episode 22.
Build transformed into TigerUFO against Grease. It could be a reference to Taiga (which sounds like Tiger) Nobori who used the UFO-like Sagarc Belt. Both Otoya and Taiga wielded the power of Dark Kiva. Aside from a UFO, Sagarcs also have features of a Cobra (again, organic-inorganic motif) and relates to how it was given by the cobra-themed Blood Stalk.
The transformation into RoseCopter can be a reference to the Queen Thorn Fangire who is the AR version of Pearlshell Fangire II who succeeded the first one with whom Otoya had an affair. Also, every member of the Checkmate Four has a rose in their sigil.
You can form the word Fangire from FanGiraffe if you don't repeat any of the letters.
There was a theory that Build would be based around model kits and in some ways, aside from the runners during transformation, it still fits.
Best Match forms are like snap fit/straight assembly models where you assemble parts that are from a single kit and are meant to go together.
Trial Forms are like when models are kitbashed and parts are taken from different kits.
Sparkling could be a reference to custom painting and detailing or an official redesign of an old kit.
Sclash sounds like scratch and scratch building is when you build a model or parts of it from raw materials. The higher hazard level required and aggression caused by the Sclash Driver can be related to how scratch building can be trying to newbie modelers.
Hazard Trigger can be related to Choking Hazard that comes up as a warning in model kits due to small parts that make it Harmful to Minors. The forms from this being black might be a reference to Ecopla.
The crack motif with Rogue could be related to Crack Is Cheaper, as some modelers buy bootleg instead of original kits. Additionally, it could represent a model with pieces that are broken and then repaired.
With the debut of RabbitRabbit and TankTank, the Hazard forms are now basically figures stripped of their removable armor, also explaining why the Hazard forms seem incomplete and completely black: it’s basically one giant undersuit. And collectors get enraged should any piece goes missing, resulting in them removing the armor set and putting them away elsewhere.
In episode 21, it's fitting that the bottles Sento used to transform again after his Heroic B.S.O.D. due to killing Aoba is Phoenix and Vacuum. Phoenix represents rebirth, and vacuum represents cleansing.
Again in episode 21; Sento hesitates for a while mid-transformation, after the Build Driver says "Are You Ready?", and the transformation only proceeds once he says "Henshin". This shows that, in this case, the 'henshin' call isn't just a catchphrase and the belt phrases aren't just to be flashy- the Build Driver is asking the user to verbally confirm that they're ready to proceed with the transformation.
Why are the Hazard forms more or less identical minus the eyes? Because it was likely never finished given Takumi Katsuragi considered it too dangerous to ever be used and unlike the Sclash Driver Sento didn't modify and finish it. It's pretty much an unfinished prototype, so it'd logically be rather bare bones.
It could also be in reference to how the Snap Ride Builder for the form is an injection mold template, since no matter what (Fullbottle) materials you use, it creates the same shape.
Why does the Hazard Trigger during transformation shout the words "Uncontrolled" and "Yabei" (Typically translated as "This is bad!")? Even Takumi thought it was too dangerous, this transformation call is a warning for everyone to get out of the way.
Adding onto this, it could be why the standby noises are so cacophonous: the suit, sans the eyes, is jet black and thus harder to see in low light conditions and the user is completely silent when berserk. Having such a loud standby noise will let anyone around know where Build is and where to avoid.
"Yabei" can also be used informally to mean something good or cool, similarly to how the word "bad" is a negative word that can be used positively. This is why RabbitRabbit and TankTank keep the "Yabei" yell, but follow it with a compliment about the chosen form's strength.
Sento acting more gung-ho and energetic and even using the Hazard Trigger during the Raising the Hazard Level special may seem jarring considering it takes place after #21, but it makes more sense when you consider his opponents are specifically Hard Light Holograms and not people he runs the risk of killing on accident.
Why is it one of the trial forms we see using the Santa Claus Fullbottle is SantaTelevi? Christmas specials.
Fullbottles don't seen to follow the science theme of the series, being soda or water bottles, but they do. They look like sample vials!
Not only that, the RabbitTank Sparkling Fullbottle resembles a jar for vitamins and the Full Full RabbitTank Bottle looks like a test tube.
Sclashjellies resemble bags for intravenous therapy.
The Genius Fullbottle could be a centrifuge.
If Fullbottles are water bottles and RabbitTank Sparkling is a soda can, then it makes sense that Sclashjellies are juice pouches and the Full Full RabbitTank Bottle is an energy drink can.
The Genius Fullbottle has the essence of every Fullbottle, making it a soda fountain.
Misora can be a transliteration of the Japanese pronunciation of the syncretic god Mithra (think Asura's Wrath), who is a War God like Mars but also a god of the sun, light, goodness, courage, friendship, truth, order, and justice. It's also a root word for the term Mithridatism, from Mithridates (a name that means "given by the deity Mithra") VI of Pontus, which is the practice of protecting oneself against a poison by gradually self-administering non-lethal amounts and Mithridate, a semi-mythical medicine, referencing her healing powers.
The positive qualities mentioned of which Mithra/s is a god of can also be associated with hope, which is what remained in Pandora's Box.
Something About a Rose and escaping by helicopter are oft-reused aspects of the Phantom Thief. It's a lovely coincidence that RoseCopter debuts on the same week as Lupinranger VS Patoranger.
The entire storyline after Hokuto declares war with Touto is very definitely making a statement on the pressures and horrors of war that are put on its soldiers and its victims, but the most interesting addition to the equation is the Sclash Driver, which seems to be a take on soldiers who become desensitized to fighting the enemy or violence in general, as well as the pressure put on them to keep going. Fullbottles won't work with it normally; only Sclash Jellies will do, and the only two that are known to exist are Robot (Known for being emotionless performers of a given task) and Dragon (Known as being cool, powerful creatures of destruction.) Compared to the Build Driver, the Sclash Driver sounds far more aggressive and badass, and the jellies are smashed by two pneumatic presses in the driver itself. They also have a dangerous issue of causing an adrenaline rush in the brain that drives the user to get in constant fights no matter how dangerous it is to their body or their mind. The only Fullbottle known to work with the driver and induce a transformation is the Crocodile Fullbottle, which is heavily cracked, and is currently in the possession of a man who submitted himself to hellish training conditions and broke himself trying to fit into a mold he wasn't entirely prepared for: being a soldier. Or in this case, a Kamen Rider.
In the fight in Touto Engineering Factory in Episode 25, Build transformed into the all-red Rose+Firetruck form and fought together with the bluish Cross-Z Charge and yellowish Grease. They're using the most used ranger colors of Super Sentai, showing that they finally became a team after their earlier conflict. Not only that, but they've become their own Hokuto Crows.
Also, continuing the Sentai tradition, Gentoku/Rogue is a mostly purple rider - what's one color that's been recently used for the Sixth Ranger as of late?
Being called Kamen Rider is a serious business in Build, only reserved to selfless, heroic people and given to them by someone else. Sento has a bit of an ego, but is overall sweet, kind person. It was later revealed that Kasuragi Takumi who despite his heartless and emotionless attitude originally developed the Rider System in order to defeat and destroy Evolto and carry on his dead father's goal. Ryuga counts too, even though he can be a jerk about it and his ways often oppose Sento to explosive results. Kazumi has to be viewed from the point of the Three Crows as he indeed is selfless and heroic to them. So why Gentoku is a Kamen Rider? Simple, he thinks he is the hero of the story and he calls himself so. Then comes The Reveal that he IS one ever since his Hazard level nullified the Hate Plague as more of an Anti-Hero who wants to unite the country so his father can run it by playing the villain.
It should be noted that the only riders that are truly evil are the ones using the Evol Drivers such as Evolt and Utsumi and Shinobu Katsuragi as the other Build, because the Rider System the other riders are using are based on the Evol Drivers and Shinobu is the one to start its development. This means they are truly fighting against the evil origins of their drivers and showcase the Phlebotinum Rebel trope which is repeatedly shown in the entire franchise.
The Hazard Trigger is the last piece of equipment that Katsuragi ever designed for Project Build before he attempted to quit Faust. Its effects are in many ways a mirror of his own stoic personality and the path of revenge that led him to create it: the device doesn't make the user into a frothing berserker, but rather makes them eerily calm and absolutely silent as they attempt to murder every living being in sight. The specific reason that Katsuragi tried to quit Faust is yet to be revealed, but it's not a stretch to imagine that he saw his reflection in the Trigger and recoiled at the sight of what he'd become.
All of the Riders each seem to resemble (sometimes inverted) parts of the Mad Scientist setup.
Build is the Mad Scientist himself, designing all of the weapons and gear that move the plot forward.
Cross-Z is The Igor, being the strong but dumb sidekick and right-hand man to Build.
Grease, using the Robot Jelly, represents the gizmos and machinery used to make the monsters, or even a Killer Robot on his own.
While he isn't this at first, by the time Rogue gets a Driver all his own, he fits the model of Frankenstein's Monster, an experiment gone rogue that intends to kill the scientist responsible for its birth.
Looking back, one can observe that whenever Sento is under pressure, he shows a lot of Dissonant Serenity as a coping mechanism. Taking this into account, the fact that Takumi Katsuragi is almost always in this state could mean that his father's death had such a negative effect on his mental health he was stuck in this state for what appeared to be several years, until his own 'death'.
Of the 4 heroic Kamen Riders, Gentoku stands out for being the only one not to have a Kanji for a certain animal in his name - Sento, Ryuga, and Kazumi have the respective kanjis for To (Rabbit), Ryu (Dragon), and Sa (Monkey)note from Sawatari. He's also the only one to start off outright villainous, and the only one who uses a Sclash Driver but not a Sclash Jelly.
The initials of Cross-Z Magma sounds like "caesium", an alkali metal that violently combusts upon introduction to the air, even more so than it's brethren.
We see a constant running gag that Owner has no clue how to make coffee, even to the point of Sento questioning why he has a shop at all. It makes sense that an alien has no clue about human tastes and food.
In the early episodes, most of the battle setup had Sento vs Night Rogue and Ryuga vs Blood Stalk. Then it turned out the match between Ryuga and Stalk makes sense given they are both aliens.
Episode 35 bring us a new light about why Evolt-possessed Souichi Isurugi named memory-deleted Takumi Katsuragi with the face of Tarou Satou as Sento Kiryuu. Not only because manipulative nature of Evolt to renaming Takumi just like the last season's big bad does as Sento's name consisted of the first kanji of 戦車 / SENsha / tank and 兎 / TO / rabbit, which literally means "war rabbit" or "war hare", exactly what RabbitTank is, but also because Sento is a kana away from "Sentou" / 戦闘, which properly means "war" or "battle". In episode 35, Evolt keep ranting Sento's belief of humanity and science, said that science only makes war in the end. The fact that Evolt-possessed Souichi before and after The Reveal always encouraging Sento to create more new equipment, and also his speech to Sento about the difference between Sento and Ryuuga before he gave Sento the Hazard Trigger, concludes in two things: He made Sento a personification of War, and he personally nurtured the War itself!
In Episode 36, Sent's form when possessed by Evolto consists of his white hair and occasional red eye. It seems to stand out compared to when Evolto posseses Banjo and Soichi, but there is a reason why. There are rabbits that are not only white in color, but said rabbits have red eyes!
With the exception of the Drill Crusher (as it can be used by any form), all of Build's weapons that were built by Sento are used by forms that either have a "weapon-based" fullbottle (the Hawk Gatlinger for Gattling and the Fullbottle Buster for the FullFull RabbitTank Bottle's TankTank mode) or a "human-based" fullbottle (the 4Koma Ninpoutou for Ninjya and the Kaizoku Hassyar for Pirate)
The Dragon Evolbottle was made from Ryuga with Evolt's power, so naturally he'd be even more synched with it than usual, and an Evolbottle is basically a Fullbottle+. No wonder he went up in Hazard Levels so fast.
Kazumi's family owns a potato farm in Hokuto. Why potatoes? They are easier to farm on poor soils than other crops (corn, wheat). Soils in Hokuto were contamined by the Sky Wall Incident, causing agriculture to go down the tubes. It was only logical to resort to crops that could handle these conditions and still provide food for the populace.
At first I was confused by the suit of Kamen Rider Mad Rogue. In my mind it didn't really have the proper colors for the bottles it used. It only had a little purple and was mostly white, contrasting how the Bat and Engine bottles are purple and red, respectively. Then it hit me; Utsumi previously used the Faust Bat bottle (purple) and the Gear Engine (white) before. Both of those carry the essences of the original Full Bottles, but still 'stained' his body enough so that when the Evol Driver gave him a form, it was altered based on the other versions rather than the originals.
Also, remember that Katsuragi mentioned the Build System is to create whereas Evolt and his Driver represents destruction? Using a Best Match in Evol Driver doesn't create a half-to-half configuration like Build, instead, a symmetrical form was made because the Driver scrambles and mix them back into a single Rider. This is to indicate that something that was purposed for destruction cannot be used as an object of creation.
When the opening got updated in #29 to include Sawa and Kazumi. At first I was confused at the begin part with the characters showing up in the screen molds being Ryuga, Misora, Kazumi, Sento and for some reason Gentoku who is an enemy at the time instead of Sawa who has cemented herself as part of their family. But after #36, it became clear that they represent the people who can fight and oppose Evolto directly. Four of them being Kamen Riders and Misora having the powers of the Queen of Mars, Vernage.
Takumi reappearing and possessing Sento's body again before Sento came back to achieve his final form was this season's way of doing the 'kill the Rider-resurrect him before final form' gimmick.
The three people affected by the light of the Pandora's Box, Gentoku Himuro, Yoshiko Tajimi and Masakuni Mido later become what they developed for the war. Gentoku focused on developing the Rider System so he became a Kamen Rider. Yoshiko focused on developing more powerful Smash so she became a Smash. Masakuni developed nothing for the war so he literally became nothing.
Another possible reason Takumi cannot use the Genius Bottle? When we see inside the head of the man, we see that the gears in his mind have stopped and they only start moving again when he gives control back to Sento. Takumi was also too focused on his goal of defeating Evolt, to the point he was willing to kill Banjou on the off chance he turns back into Evolt, that he created dangerous inventions like the Hazard Trigger, inventions that could only be used as weapons. The Genius Bottle didn't recognize Takumi, who became a demon unable to think beyond his goal of defeating Evolt, as a true genius. The more heroic Sento, who truly thinks about others and uses his intelligence to better mankind, was the one who truly deserved the title of Genius.
The Hazard Trigger and the Genius Bottle could represent the two kinds of scientists. The Hazard Trigger represents scientists like Takumi or Utsumi who pursue science and do all kinds of experiments simply cause it interested them or stroked their ego, possible repercussions be damned, and one day, they'll find their experiments go out of control. The Genius Bottle, however, represents scientists who use their intelligence to better all of mankind and refuse to do less than moral experiments for science's sake.
Of course Banjou has no brains, Evolt is the one who got all the brains when they became individual beings.
Most of the transformations, even the more higher tier ones, use only one or two Full Bottles at most. So what does that say about the strength of Build Genius, which has sixty Full Bottles directly attached to the suit?
Kamen Rider Rogue's "broken" motif, on one level, represents the harsh treatment that Gentoku had to undergo to raise his Hazard Level and become a Rider. On the other hand, it could also represent kintsugi, the Japanese technique of repairing broken pottery with gold, to embrace the imperfections and flaws. Referring to the fact that Gentoku's breakdown was necessary for him to throw off the influence of Pandora's Box and eventually become a hero.
After seeing Gentoku's choice of clothingafter being freed of the influence of Pandora's Box. It makes sense why he used to sit on that incredibly tacky chair as Night Rogue.
With the revelation of the true nature of the Best Matches revealed in Episode 41, it suddenly makes a lot of sense why so many of the Best Matches seem like random combinations. It's because they mostly ARE completely random combinations!
With the information that Best Matches are really thirty things Misora liked being destroyed by thirty random weapons and objects, how do some of the more random combinations like Lock and Dragon or Unicorn and Eraser fit this new theme?
Dragon and Lock: Dragons are traditionally written to live in caves filled with their treasure. Locking up the entrance would mean the dragon would be stuck in the cave and starve to death.
Unicorn and Eraser: Unicorns are fictional creatures and so, they usually only exist as drawings drawn by a young girl like Misora used to be. An eraser would be used to cruelly erase a little child's drawing of a unicorn.
Phoenix and Robot: A beautiful and fantastical bird that is free to fly wherever it wants is killed by a completely non-magical and cold weapon that only does what it is told to do.
Rose and Helicopter: Imagine a beautiful field of blooming roses. Now imagine it being cut down by the blades of a helicopter.
Octopus and Light Bulb: Put a octopus under a heat lamp and sooner or later, it will dry up and die.
Pirate and Train: A pirate is utterly powerless to stop a land vehicle like a train and will be ran over by it.
Ghost and Magnet: A ghost's existence may be proven false by skeptics claiming magnets were used to simulate the effects of a haunting.
Ninja and Comic: A ninja could have their name publicized, leading to someone tracking them down and finding them.
Hedgehog and Firetruck: It's very possible the water pressure from a firetruck's hose could kill a hedgehog. Either that, or the firetruck can just run over the hedgehog.
Dog and Mic: Dogs have sensitive hearing, so shouting loudly into a working and plugged mic would be disastrous to them.
Turtle and Watch: As old as turtles can live, they can still die to old age.
Spider and Refrigerator: Spiders will freeze to death if you put them in a fridge.
Whale and Jet: A jumbo jet can lift up a whale out of water, slowly killing them like a beached whale.
Deer and Pyramid: Pyramids are found in deserts, and deers can't live in deserts.
Scorpion and Gold: A gold bar is very heavy. Drop one on a scorpion, and it goes splat.
Wasp and Submarine: Submarines are made for underwater exploration, while wasps aren't.
Observe the almost casual ease that Blood Stalk, Night Rogue, and Build are able to mow down soldiers, be they human or robot. Now, consider the fact Night Rogue's ultimate plan is an entire army of Dark Riders. We've seen armies of Riders mow down armies of monsters, but this series highlights just how utterly screwed humanity would be if that army was against them.
Since the opening of the Pandora Box made everyone present have their aggressiveness and other negative traits within them magnified you wonder if some of these people were once decent and nice people before the Sky Wall Disaster eventually turned them into worse people. Makes you wonder if people like Gentoku and Souichi were once decent people before the Pandora Box was involved, with even Souichi admitting that the Pandora Box did a number on his mind when he touched it.
Confirmed with Gentoku and Yoshiko. When they both got cured of the Hate Plague they had a big My God, What Have I Done? moment and now have to live with what they did. While Souichi was possessed all the time by an evil alien that wants to destroy the planet.
Misora is needed to purify Full Bottles, and yet a large number of them would only form in the other two capitols. Does this mean there are at least two other people like her out there being subjected to similar horrible treatment and manipulation in the other two capitols to purify their Bottles?
Either that, or else Misora purified all the bottles, and Souchi..."dispersed" them while setting up the plan to make Touto's set.
Despite how much of a genius physicist Sento is, his amnesia actually makes him disturbingly similar to Misora; they're both children inside, despite their older bodies. Misora never got the chance to grow up, and Sento has to grow up from scratch. He's technically only one year old at best. They're both children who are thrown into a conspiracy and eventually they're in a war they wanted no part in, but directly blame themselves for and Sento ends up killing someone.
The fact that it was Souichi who named Sento takes on a new twist with his attitude that the Riders are simply weapons, after all he literally named him "Rabbit Tank"
Its more Fridge Squick but we cannot deny that Banjo's origin story involves an alien slug thing slithering into a woman's vagina.
Not likely, as Stalk intended to possess Banjo's mother himself, but did not account for her pregnancy.
Most likely Sento Kiyruu would come back but that would mean Takumi Katsurgi would had to "disappear/die" again as all intents in purposes they are really more like separate people in the same body. While it would be great for the Nascita crew, friends and allies as Sento can handle the Build System better at its current state and they trust Sento more the fact that Takumi would had to technically speaking have to give up his existence so the person the crew want would be back is kind of sad. He didn't choose to lose his memory and his face be changed and lose his identity as Takumi. Maybe Takumi wasn't the greatest person in the world but he wasn't totally heartless either and being erased like that its kind of unfair to him.
slightly downplayed compared to how you wrote it. He isn't 'gone' per se, rather he's become one with Sento, albeit with Sento as the dominant mind in the fusion. The ultimate difference between Sento and Takumi is their experiences and how the world has treated them. Takumi lived a life of ridicule and humiliation from his father being attacked from the Skywall disaster and his suicide. Sento has had support from Souichi and Misora most of his 'life' and was given a heroic ideal to follow. They are the same person in almost every other regard, and ultimately Sento's heroic determination and trust in his friends meant that he's the one needed to control the fusion. Technically parts of Takumi still exist inside of Sento, but we may see them more as the show goes on or in the movie.
If Evolt dug deeper into Souichi's mind to find thirty real weapons, what are the chances he would've found one of the worst and destructive weapon humanity made, the nuclear bomb, and made a Full Bottle out of that? Souichi and Japan were lucky Evolt decided to accept the answers Souichi gave him or there might've been a Nuclear Bomb Full Bottle out there.