This article is about a/an monster race in Kamen Rider Build.

The Smash (スマッシュ Sumasshu) are a type of monster created by the experiments conducted by Faust. Sento Kiryu fights them as Kamen Rider Build and uses their essence to create more Fullbottles.


The Smash are humans who have been injected with the Nebula Gas as part of Faust's experiments. Nebula Gas is able to trigger rapid cell division and turn a human into a monster. Moonsault of Anger Each Smash is the basis for an equivalent Fullbottle. A Smash has superhuman abilities, but possess little to no human consciousness.

The technology used to create the Smash is implemented in the Steam Blade. By using its Devil Steam function, it can turn any human into Smash in a more convenient way.

In order to restore the Smash back to normal humans, the Kamen Riders must defeat them and absorb the Nebula Gas into an empty Fullbottle. Misora Isurugi is known to be able to "purify" the Smash essence with her gold bracelet, which allows the Riders to use the Fullbottles with their equipment.

A side effect of the Smash transformation is short-term memory loss.That One with the Best Match It seems only humans in peak physical condition can handle the transformation into a Smash, as shown with Kasumi Ogura, who suffered from an unspecified illness; removing the Smash essence is fatal to Smashes created from frail humans. The Innocent Runaway Similarly, there seems to be a limit as to how much Nebula Gas a human can absorb: Masahiro Nabeshima and Tatsuya Kishida, who both received excessive amounts of Nebula Gas, would have died from their overdoses if the Riders were too late in removing their Smash essence. (This death is fully shown with Shingo Kuwata after his second dose.) The Trap of Project Build

Certain Smash forms have reappeared in either the same or stronger (Hazard) forms in multiple people.



Faust began Smash experimentation no later than 9 years after the Sky Wall Disaster. Through these experiments, numerous humans were transformed into Smash monsters after being exposed to Nebula Gas. Released to run amok, they were intended to be fought by the Kamen Riders, a potential weapons system.

A Square Smash was the first to be defeated by Sento Kiryu, who became Kamen Rider Build via the Build Driver and Fullbottles provided to him by Soichi Isurugi. Who Takes Off The Veil?

The attacking Smash ultimately became notorious enough that they were noticed by the general populace, with journalist Sawa Takigawa investigating them. She herself would be attacked by the Needle Smash, but saved when it too was defeated by Build, who freed its host by extracting the Smash essence.

Convict Ryuga Banjo was exposed to Nebula Gas, but did not become a Smash due to his high Hazard Level. Escaping the clutches of Faust, he was pursued by the Strong Smash, but was protected by Sento Kiryu, who defeated the Smash but unable to gain any information from the host Shimizu due to amnesia caused by the process. That One with the Best Match

Soona after, Ryuga's girlfriend Kasumi Ogura was kidnapped and transformed into the Burn Smash. As revealed by Faust executive Night Rogue, since Kasumi was only at Hazard Level 1, she would die should the Smash be defeated. Nevertheless, Build was ultimately forced to terminate her to end the Smash's rampage. The Innocent Runaway

Reika Kine was transformed into a Flying Smash. Going on a frenzy, the Smash tried attacking Reika's son Kota before being fought back by Build. The Flying Smash was eventually defeated by Build GorillaMond, returning Reika to her human state, to the joy of her and her son.

A pawn of Faust, Masahiro Nabeshima was transformed into the Mirage Smash. On his rampage, he attacked a group of Touto Guardians and Sento, fighting Build RabbitTank by duplicating himself. After Build switched to HawkGatling and defeated him and all his duplicates, his Smash essence was extracted. However, he was taken away by Blood Stalk. Borderline of Justice

Nabeshima was injected with Nebula Gas again, transforming into a second Square Smash. He was set upon a park, coming to blows with Build once again. After fighting for some time, Blood Stalk fired upon him with his Steam Rifle, causing him to grow in size. Build proceeded to defeat him with the Full Bullet finisher, and upon having his Smash essence extracted returned to normal once again. The Testimony Will Be Zero

To lure Sento out, Blood Stalk kidnapped Tatsuya Kishida and had him turned into a Press Smash. Though Tatsuya was returned to normal by Build NinninComic Form, he soon reverted to his Smash form as Ryuga knocked Sento out to use the Smash to find Faust's secret location. The Press Smash's Hazard Level had been increased to cause his body to go haywire and almost destroyed, until Build NinninComic Form saved him during his and Ryuga's raid on Faust's secret lab. Dangerous Identity Moonsault of Anger

In Hokuto, Blood Stalk used the Steam Blade's Devil Steam to transform a young boy named Takehiko into the Ice Smash. He was soon purified by Build, although the stress from transforming into a Smash put a huge toll on his body. The Devil's Scientist

Kidnapped by Night Rogue, Takumi Katsuragi's mother Kyoka was transformed into the Strong Smash Hazard, first of the stronger Hazard Smash, but was freed by Build FireHedgehog Form. Memory Starts to Talk

Revealing himself as a Faust member, Shingo Kuwata willingly transformed into a Flying Smash by pouring an unpurified Fullbottle onto himself, becoming the Smash to fight Build and lead him away from the Touto Institute of Advanced Matter Physics so Faust could attack without his interference. He was eventually defeated by Build LionCleaner. The Trap of Project Build

Exposed as a spy, Sawa was transformed into the Stretch Smash by Faust, but was pacified by Kamen Rider Cross-Z with the Smash essence extracted by Build. Burning Dragon

On November 30, 2017, a Strong Smash Hazard attacked Sougo Tokiwa, who had been accidentally deposited into the World of Build timeline. Sougo was saved by Kamen Riders Build and Cross-Z, who performed their respective Vortex Finish attacks to destroy the Smash. Kingdom 2068

Revealing himself to be Night Rogue, Gentoku Himuro transformed a pair of Touto soldiers into a Strong and Stretch Smash Hazard. They were pacified by Kamen Riders Build and Cross-Z. Judging Sento Kiryu!

Two unidentified individuals were transformed into a Press and Flying Smash Hazard, and were sent by Hokuto to run amok as part of their invasion of Touto. They were pacified by Cross-Z and Build. The Weaponry Hero

Hard Smash

Main article: Hokuto Sanbagarasu

Akaba, Aoba and Kiba, originally workers of Kazumi Sawatari's farm, enlisted into Hokuto's military as the Hokuto Sanbagarasu to repay their former employer's debt after a severe drought struck the area and Kazumi chose to financially support his workers' families. Using Lost Fullbottles supplied by Namba Heavy Industries Ltd., they were able to transform into the superior Hard Smash. Unlike prior Smash, they were able to retain full control of themselves while transformed and fought as soldiers of Hokuto.

Seeking greater strength to repay Kazumi, the Hokuto Sanbagarasu volunteered to be administered with the Hazard Trigger's energy. Though they became the more powerful Hazard Smash, the price was that being defeated would result in death. The Forbidden Item

Tragically, Aoba became the first of the Hard Smash to die when the Hazard Trigger was used by Sento himself to access the Hazard Form of Kamen Rider Build. The use of the device caused Sento to loses his senses and he did not hesitate to defeat the Stag Smash Hazard. The Unstoppable Hazard

With Hokuto's forces focused in Touto, Seito used the opportunity to invade Hokuto. Returning to defend his home, Kiba found himself overwhelmed and captured by Seito's updated Kaisers, Engine and Remocon Bro's, who completely outclassed the Hard Smash. Though Kazumi and Akaba arrived to rescue Kiba, they fared no better and a gravely wounded Kiba ultimately gave his life to save Kazumi from Remocon Bro's, leaving Akaba as the last known Smash. The Phantom of the West

Akaba would later be killed by Kamen Rider Rogue, while guarding Pandora Box, leaving all three Hard Smash deceased. The Idol Awakens

Clone Smash

Through data collected from a battle between the Clone Hell Bro's and Sento Kiryu, Kamen Rider Build: Raising the Hazard Level ~7 Best Matches~: Final Chapter Nariaki Utsumi developed a new breed of Smash: the Clone Smash. These Clone Smash were distinct in that they were created without the use of a human host and were more resilient as they lacked a sense of pain. However, they still lacked the intelligence of the Hard Smash. The first pair, the Press Clone Smash and the Stretch Clone Smash, were summoned by Blood Stalk to fight Build and Grease during the battle for the Pandora Box. They were ultimately destroyed by Ryuga Banjo when he used the Cross-Z Magma Knuckle to become Cross-Z Magma. Surging Magma!

A Strong Clone Smash was seen accompanying Utsumi before being easily destroyed by Kamen Rider Rogue. The Final Weapon: Evol

A Flying Clone Smash and a second Strong Clone Smash were summoned by Evolto alongside a pair of Hard Guardians to fight Build and Grease. The two Clone Smash were soon destroyed by Grease's Scrap Finish. Evolto Hunts Stars

Lost Smash

A new type of Smash created from Evolto's experiments with the help of Shinobu Katsuragi, the Lost Smash is described as the "final form" of a Smash. A human subject is injected with a heavy dose of Nebula Gas, allowing them to fuse with two Clone Smash via the usage of a Lost Fullbottle to transform into a Lost Smash. This has the side effect of the user becoming more aggressive and easier to control. Also, the heavy dosage of Nebula Gas means that the human subject would usually die upon the Lost Smash's defeat.

Kamen Rider Build's Genius Form is able to neutralize the Nebula Gas within the Lost Smash, enabling him to defeat them without killing the human host, instead reverting the human host back to their original personality with the Lost Fullbottle turning completely black and unable to be used. Once inserted into the Last Pandora Panel of the Pandora Box, this inert Fullbottle becomes a Black Lost Fullbottle. Evolto aimed to use the Lost Smash to complete the Last Pandora Panel and kept the Kamen Riders alive for this purpose, either to defeat Lost Smash for him or be turned into Lost Smash themselves. Once ten Black Lost Fullbottles are inserted into the Last Pandora Panel, Evolto can assume his monster form.

A person can alternatively transform directly into a Lost Smash without the need for two Clone by using a Black Lost Fullbottle. Unlike those made using the former method, these Lost Smash are in complete control of themselves.

Known Smash

Known Empowered Smash

Known Hard Smash

Known Hazard Smash

Known Clone Smash

Known Lost Smash



All of the Smash are designed by Tamotsu Shinohara.


  • Smash appear to have two unique base bodies (visible as the legs) that their identifying features are attached on top of - a smooth, plated, pointed body, and a mechanical body. This suggests a pattern regarding which Fullbottles (biotic/abiotic) come from which Smash, but in practice there is no specific pattern.
  • Smash bursting into green flames upon defeat and having their essence sealed away is reminiscent of Kamen Rider Blade Riders sealing the Undead away. The main difference being that the Undead are completely locked away into the cards, while the Smash have their Nebula Gas elements sealed away and turned back into normal humans instead of being completely locked away.
  • Smash carry elements of prior antagonists, while being separate from the others by tweaking aspects of said elements:
    • A result of malicious experiments like the Amazonz.
    • Generals/Leaders either possessing Rider-like abilities or actual Rider forms, or enlisting enforcers with the same traits like the Gamma and Roidmudes.
    • Rare instances have occurred where the subject can retain their humanity and switch between both forms at will like the Over Lord Inves.
    • Their powers being utilized for Form Changes like the Undead and Greeed.
  • The Hazard-variant Smash are one of the few instances where the body shape of the upgraded/enhanced antagonist monsters is left unaltered, with the visual difference being seen in the coloring, darker colors being a consistent aspect. This concept was last seen in the Neo Heisei-era with the Super-Evolved Roidmudes.



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