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Icon-build.png This article is about a/an ally in Kamen Rider Build.

Aoba (青羽), born Syuuya Aikawa (相河 修也 Aikawa Shūya), is one of the boys who hailed from Hokuto, part of the Hokuto Sanbagarasu led by Kazumi Sawatari. He was able to change into the Stag Hard Smash (スタッグハードスマッシュ Sutaggu Hādo Sumasshu)[1] using the Kuwagata Fullbottle. Later, after being administered the Hazard Trigger, he became the Stag Hazard Smash (スタッグハザードスマッシュ Sutaggu Hāzado Sumasshu).


Becoming Aoba

Aoba was originally a farm worker in Hokuto, employed by Kazumi Sawatari. After the Sky Wall Disaster, Hokuto's farm land was rendered unsuitable for crops. Sawatari spent all of his savings to continue providing for his employees and their families, and volunteered himself for Faust's experiments when his funds were depleted. Feeling indebted to Sawatari, Aoba volunteered himself as well, becoming a Hard Smash in the process.

Invasion of Touto

When Hokuto Prime Minister Yoshiko Tajimi declared war on Touto, Aoba was part of the advance guard with Kiba and Akaba. As Kiba watched a live stream of inferior Smash being defeated by Kamen Rider Build, Aoba attributed their weakness to their lack of awareness. The Weaponry Hero

Aoba and the others later tracked down Sento Kiryu and Ryuga Banjo, and transformed into their Hard Smash forms. After successfully knocking them out of their transformations, Akaba demanded that they hand over their Fullbottles, prompting Aoba and Kiba to argue with him over who should get said Fullbottles. By the time they had pulled themselves together, Sento and Ryuga had absconded.

Later, they found Sento consoling Misora Isurugi as she lamented her role in allowing evil to wage war, and told Sento to hand over his Fullbottles. This time, Sento gave them a challenge with a determination he gained from Misora, using RabbitTank Sparkling Form. However, Akaba, Aoba, and Kiba still quickly gained the upper hand, until Ryuga appeared with the Sclash Driver and transformed into Kamen Rider Cross-Z Charge. Ryuga and Sento easily defeated them, causing them to drop the Phoenix, Robot, Wolf, Smapho, Kuma, and TV Fullbottles. Kazumi Sawatari arrived shortly after to challenge Sento and Ryuga. Rider Wars Start

Alongside Kiba and Akaba, Aoba interrupted a fight between Grease and Cross-Z Charge, only for Kazumi to state that they had broken the rules of engagement and relinquish the Kuma and TV Fullbottles to Ryuga as his penance. Soon after, the Hokuto Sanbagarasu received dog tags from Kazumi which had finally accepted from Massugu Ubukata, whom crafted them out of respect; befitting the Stag Hard Smash, Aoba's tag was colored blue. Kamen Rider Build: Birth! KumaTV!! VS Kamen Rider Grease!


"I'm worried...If I'm not around...You can't do anything, Boss. No matter what happens...We're together..."
―Aoba's final words to Kazumi.[src]

The death of Aoba.

After Sento accessed Build's RabbitTank Hazard Form, the fight leads to an abandoned warehouse, with Aoba engaging Ryuga and Sento overpowers Akaba and Kiba in their Hazard Smash forms. During his attempt to stop Cross-Z Charge, Build fell into a rampage due to the Hazard Trigger's side effect and started attacking both ally and foe alike. As Build knocks Akaba and Kiba outside, Aoba attempts to aid his comrades but is easily swatted away by Build. After his assaults forced Castle and Owl to revert to their human forms, Aoba became the first victim of Sento's rampage after receiving a direct hit of Build Hazard's Overflow attack, with Kazumi transforming into Grease but too late to stop Build from unleashing a Hazard Finish attack. After Kazumi cancels Sento's form, he goes to Aoba's side as his body begins to disintegrate. He hands over one of his tags, the one with his name, to Kazumi and gives his last words before dying, with his body completely disintegrated into a blue smoke. His death shocked Ryuga and Sento, while Akaba and Kiba were filled with sorrow for their slain comrade and rage towards Sento.

A week later, as he went back to the location of Aoba's death to pay his last respects, Sento would be greeted by a vision of Aoba, which frightened him due to his guilt. The Unstoppable Hazard


Giving his life to save Kazumi, Kiba ripped off the dog tag bearing his name and left it to Kazumi just as Aoba did before his death. Before passing away, Kiba told Kazumi he would watch over him from beyond beside Aoba. The Phantom of the West

In respect for Aoba and Kiba, Sento left a bunch of blue and yellow flowers at the sight of the former's death in Touto, which Stalk took as Sento shouldering their deaths. Soon after, Grease arrived to save Sento from going berserk after using the Hazard Trigger in his fight with Stalk, claiming it was thanks for the flowers. A Man Called Rogue

Akaba proposed to Kazumi that Aoba and Kiba's dog tags be buried at the Sky Road passage between Touto and Hokuto. Before they could tend to this, however, Akaba was confronted by Kamen Rider Rogue while guarding the Pandora Box and, despite calling on the power of his late teammates, was killed in action, leaving his and their dog tags to Kazumi. The Idol Awakens

Kazumi crafted a grave for the Sanbagarasu at the Sky Road. However, he held onto their dog tags as he participated in the Proxy Battle against Seito where, despite being outmatched by Engine Bro's, he was ultimately motivated to overcome his opponent by looking back to his late comrades. The Treacherous Deathmatch Kazumi would continue to fight to ensure the well-being of the late Sanbagarasu' respective families. The Counterattack Hero

New World

Sanbagarasu with Kazumi in the new world.

Aoba's appearance in NEW WORLD.

Aoba, along with his friends, were among the few people who has a counterpart on the World without Sky Wall, and was seen as one of the delivery men who frequents Nascita. On one occasion, they dragged their boss to see the cute girl from the coffee shop they frequent in, which ended up with their boss passing-out after seeing Misora.The Tomorrow Build Will Create When Killbus reactivated Pandora's Box, everyone who were directly exposed to Nebula Gas in the original World of Build regained their memories from that world, including Aoba. Although he didn't participate in the fight against Killbus, they were mentioned by Kazumi in the meeting.Build NEW WORLD: Kamen Rider Cross-Z

Because of their memories being restored, Misora's attitude towards Kazumi went back to the way they were in the original world, which worried Aoba and the others. After a misunderstanding between Kazumi and Misora, Aoba and the others did their best to cheer their boss, to the extent that they were willing to join him in his self-searching.I Heard the Idol Otaku is Dating His Fav This led them to an island which was formed from the point of contact between the two worlds that merged. Kiba felt something dangerous from the island at first, but calmed down after finding a hot spring. While they were bathing in it, a geyser suddenly emerged, which soaked the four even further to the water. After being soaked, the four went to a cave to try and warm themselves up, as they were feeling some strange after-effect from the water. They would later recover and find their way back to the Sawatari Farm, only to find it attacked by a foreigner, which Massugu described as a green monster. Confronting the perpetrator, they were confused on to what the attacker wanted to do, and was more confused when it suddenly flew away after it saw them transform. Kazumi then contacted Gentoku, who hinted that he was captured. After the call, they then went to Sento's place to find out more. Given the task to safeguard Misora, Aoba left with Kiba and Akaba, leaving behind Kazumi due to the trauma their boss still have. Arriving just before Down Fall took Misora, they were confronted by Kamen Rider Metal Build and were taken out all at once. Regaining consciousness just after Sento was explaining the power-up item to Kazumi, the Sanbagarasu waited for their boss to leave, before willingly agreed to help Sento. Sento then explained that he will need the three to give-up a majority portion of their Phantom Liquids, the extraction was painful, but they were able to gather enough for four and complete Grease Perfect Kingdom. After Kazumi successfully defeats Kamen Rider Phantom Build, Aoba and the others revealed to Kazumi that they had to play along Sento's plan to elevate Kazumi's Hazard Level by believing them to be dead, from which Kazumi calls Sento the Devil Scientist again.Build NEW WORLD: Kamen Rider Grease


Aoba is the most level-headed of the Hokuto Sanbagarasu, and seemingly the most selfish, both by a small margin. He appears to get to the point of his missions quicker than the others, but still indulges in petty quarrels such as arguing over who would take Sento Kiryu and Ryuga Banjo's Fullbottles.

According to Kazumi, before the war, Aoba was one who cared about his friends and would cry for even a complete stranger.


Stag Hard Smash

Stag Hard Smash

  • Height: 205.2 cm.
  • Weight: 124.4 kg.

Aoba transforms into the Stag Hard Smash (スタッグハードスマッシュ Sutaggu Hādo Sumasshu) using the Kuwagata Fullbottle.


  • The Stag Hard Smash is armed with the pair of sword-like Rapture Scissors (ラプチャーシザース Rapuchā Shizāsu).
  • The Stag Hard Smash can move at super speed.

Appearances: Build Episode 17-19

Stag Hazard Smash

Stag Hazard Smash

  • Height: 205.2 cm.
  • Weight: 124.4 kg.

After being administered with the Hazard Trigger's energy, Aoba can transform into the Stag Hazard Smash (スタッグハザードスマッシュ Sutaggu Hāzado Sumasshu) with the Kuwagata Fullbottle.

The Stag Hazard Smash is far more powerful that its Hard Smash form. However, this form comes with a risk: being defeated will cost Aoba his life.


  • The Stag Hazard Smash is armed with the pair of sword-like Rapture Scissors.
  • The Stag Hazard Smash can move at super speed.

Appearances: Build Episodes 19-21

Stag Lost Smash

Stag Lost Smash

  • Height: 205.2 cm.
  • Weight: 124.4 kg.

The New World counterpart of Aoba transforms into the Stag Lost Smash (スタッグロストスマッシュ Sutaggu Rosuto Sumasshu) using the Stag Lost Fullbottle.

This form is exclusive to Build NEW WORLD: Kamen Rider Grease



Behind the Scenes


Aoba is portrayed by Tateto Serizawa (芹澤 興人 Serizawa Tateto). As Stag Hard Smash, his suit actor is Kotaro Kaji (鍜治 洸太朗 Kaji Kotaro).


Aoba's name translates to "blue wings", sharing a color theme with Kiba (黄羽 lit. "yellow wings") and Akaba (赤羽 lit. "red wings"). Incidentally, his name is also phonetically identical to the phrase "blue leaves" (青葉 Aoba).

Concept Art

Stag Smash was designed by Tamotsu Shinohara (篠原 保 Shinohara Tamotsu).


  • Same as other member of Hokuto Sanbagarasu, all three name had a color name. in Aoba's case, it's ao (青) which means blue.



Icon-build.png Kamen Rider Build
Kamen Riders
Sento Kiryu (Takumi Katsuragi) - Ryuga Banjo - Kazumi Sawatari - Gentoku Himuro - Evolto - Nariaki Utsumi - Shinobu Katsuragi
Movie-exclusive: Kengo Ino - Killbus - Keiji Uraga
Drivers/Transformation Gear
Build Driver - Transteam Gun - Nebulasteam Gun - Sclash Driver - Evol-Driver
Transformation Devices
Fullbottles - (Great) Cross-Z Dragon - Sclashjellies - Hazard Trigger - Cross-Z Magma Knuckle - Evol-Trigger - Grease Blizzard Knuckle - Killbuspider - Grease Perfect Kingdom
Drill Crusher - Hawk Gatlinger - 4Koma Ninpoutou - Kaizoku Hassyar - Fullbottle Buster - Steam Blade - Beat Closer - Twin Breaker - Muscle Glove - Solstall Wings - Giant Scratcher - Space Ride Arm - Spine Knuckle - Long Range Cleaner - Trash Converter - Gold Lio Gauntlet - Multi Deluge Gun
Pandora Box - Halfbodies - Fullbottle Holder - Build Phone
Vortex Finish - Hazard Level - Project Build - Sky Wall - Nebula Gas
nascita: Misora Isurugi - Soichi Isurugi - Sawa Takigawa - Kazumi Sawatari - Gentoku Himuro
Kamen Riders: Eiji Hino - Gentaro Kisaragi - Kouta Kazuraba - Takeru Tenkuji - Emu Hojo - Hiiro Kagami - Taiga Hanaya - Kiriya Kujo - Kuroto Dan - Parado - Sougo Tokiwa - Geiz Myokoin - Tsukuyomi
Prime Ministers: Taizan Himuro (Touto) - Yoshiko Tajimi (Hokuto) - Masakuni Mido (Seito)
Namba Heavy Industries Ltd.: Juzaburo Namba - Nariaki Utsumi - Haruhiko Wanibuchi - Guardian
Hell Bro's: Fu Washio - Rai Washio - Yoshikazu Takahashi - Norio Matsui
Aliens: Vernage
Gentoku Himuro - Evolto - Nariaki Utsumi - Takumi Katsuragi - Shingo Kuwata - Eita Kawai - Yoshikazu Takahashi - Norio Matsui
Normal Smash: Fang Smash - Needle Smash - Strong Smash - Burn Smash - Flying Smash - Mirage Smash - Square Smash - Press Smash - Ice Smash - Stretch Smash
Empowered Smash: Strong Smash Hazard - Press Smash Hazard - Stretch Smash Hazard - Flying Smash Hazard
Hard/Hazard Smash: Castle Hard/Hazard Smash - Stag Hard/Hazard Smash - Owl Hard/Hazard Smash
Clone Smash: Press Clone Smash - Stretch Clone Smash - Strong Clone Smash - Flying Clone Smash
Lost Smash: Owl Lost Smash - Stag Lost Smash - Castle Lost Smash - CD Lost Smash - Scissors Lost Smash - Zebra Lost Smash
Foundation X
Kaisers: Kaisei Mogami (World of Build, World of Ex-Aid) - Nebula Bugster
Blood Tribe
Kengo Ino - Ryoka Saiga - Mitsuomi Gobara - Evolto - Killbus - Akaba (imitation) - Aoba (imitation) - Kiba (imitation) - Remocon Bro's (imitation) - Engine Bro's (imitation)
Down Fall
Keiji Uraga - Simon Marcus (Phantom Crusher)