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 Televi 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 Televi 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! KumaTelevi!! 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

New Akaba, New Aoba and New Kiba.jpg
Aoba Grease.png


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).


  • His color scheme being blue and themed after a stag beetle brings to mind Kamen Rider Gatack, the Secondary Rider in Kamen Rider Kabuto.
  • Aoba's transformation into the Stag Hard Smash by injecting the Kuwagata Fullbottle into his arm is similar to the Dopants of Kamen Rider W.
  • The Stag Hard Smash's Rapture Scissors shared both their names and design with Gremlin's signature swords.



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