This article is about a/an villain in Kamen Rider Build.
For the previous "Right Kaiser", see Kaisei Mogami (World of Ex-Aid).

―Transformation phrase[src]

"I am Engine Bro's, and my brother is Remocon Bro's. Which one do you wanna fight first?"
―Rai introduces himself and his brother to the Owl Hazard Smash. [src]

"Brother! It's up to you now! EVERYTHING... IS FOR NAMBA INDUSTRIES!"
―Rai's last words to his brother[src]

Rai Washio (鷲尾 雷 Washio Rai) was the younger brother of Fu Washio, hailing from Seito. He was able to transform into the white Kaiser, Engine Bro's (エンジンブロス Enjin Burosu).

Character History

Little is known about Rai’s past, but he and his brother were raised by the Juzaburo Namba institute as his 'Children'. There, Rai and Fu were indoctrinated and trained as soldiers.

Rai, along with Fu was first shown at Hokuto after Kiba defeats Seito Guardians as Owl Hazard Smash. They quickly defeat the latter as Engine and Remocon Bro's easily and taunt Grease to become Seito’s weapon, if he wants Kiba to live.

After they torture Kiba, Kazumi and Akaba arrive, and Kazumi rejects Rai's offer and fights him as Grease. Grease, along with Akaba and Kiba escapes, but later shot by Fu using Nebulasteam Rifle. Fu's about to kill Grease, if Kiba didn't take the bullet for him. Akaba later helps his boss escape once more, to Sky Road where Sento and Banjo awaits.

As the Washio brothers finally caught up to them, Sento and Ryuga fights them as Build Rabbit Tank Hazard (later Rabbit Tank Sparkling) and Cross-Z Charge respectively, until Rogue make his appearance. The Phantom of the West

Joining Seito's forces in an attack on the Touto government office, the Washio brothers covered Rogue as he went in to claim the Pandora Box, engaging Kamen Riders, Cross-Z Charge, Grease and Build before the latter caught up with Rogue. Eventually, the Kaisers succeeded in defeating the Sclashjelly Kamen Riders. A Man Called Rogue

Alongside Rogue, the Washio brothers represented Seito in a three-stage Proxy Battle with Touto. Fu faced Grease in the first round and initially overwhelmed the Kamen Rider only to be shockingly defeated when Grease, recalling his deceased comrades, persevered and struck back at Engine Bro's. With Rai defeated, his Gear Engine was used by Fu alongside the Gear Remocon to face Cross-Z Charge as their combined form, Hell Bro's in the second round. The Treacherous Deathmatch During their battle, Fu claimed to Ryuga that, since his brother had failed, Rai had been taken away by Seito with his survival depending on the elder Washio's victory, using the resulting hesitation in Ryuga to knock him out of the contest. Soon after, Rai arrived, having been unharmed, and gloated with his brother. The Counterattack Hero


During a heist against Evol Black Hole, both Fu and Rai are injected with Nebula Gas by Utsumi to further strenghen them, with a cost of death should they defeated. However, even with the injection and temporary alliance with Touto Kamen Riders, Evol is still too strong for them to handle. Evol then generate a Miniature Black Hole at Engine Bro's. The Black Hole not only cancels Rai's transformation but also starts to disintegrate him. Before he dies, Rai give his Gear Engine to his brother and swears his absolute allegiance for Namba Heavy Industries.Mad World


Compared to his brother, Rai was more outspoken and seems to be prideful with his abilities. He has a tendency to mock his opponent to let his/her guard down. He also doesn't hesitate to use underhanded tricks, like capturing an unconscious Misora and keeping her hostage to force Touto's Kamen Riders to relinquish their Fullbottles. Nevertheless, both Fu and Rai are cruel and ruthless, and like to torture their defeated opponents.


Nebula Hell Bro's
Nebula Hell Bro's

Nebula Hell Bro's

Nebula Hell Bro's (ネビュラヘルブロス Nebyura Heru Burosu) is the basic body of the Kaiser with no Gears attached, though it is typically bypassed altogether in the transformation into Engine Bro's.

Engine Bro's
KRBu-Engine Bros

Engine Bro's

"Gear Engine! Funky! (Rock music, engine revving) Engine Running Gear!"
―Transformation announcement[src]


  • Height: 203.0 cm.
  • Weight: 103.5 kg.

Ability Perimeters:

  • Punching Power: 30.2 t.
  • Kicking Power: 37.2 t.
  • Maximum Jump Height: 48.6 m.
  • Maximum Running Speed: 100 m. per 1.7 sec.

One half of the Hell Bro's, Engine Bro's (エンジンブロス Enjin Burosu) is the white Kaiser, transformed into by inserting the Gear Engine into the Nebulasteam Gun.

Engine Bro's possesses strength to rival Kamen Rider Grease, Kamen Rider Cross-Z Charge, and Kamen Rider Build RabbitTank Sparkling Form, only beginning to struggle with Build's RabbitTank Hazard Form. Engine Bro's, however, is not without a weakness. Being based on an engine, he can easily be damaged with water-based attacks.

Remocon Bro's and Engine Bro's share a single Nebulasteam Gun and Steam Blade. In battle, Remocon Bro's usually wields the Nebulasteam Gun while Engine Bro's usually wields the Steam Blade.

Engine Bro's has 3 different finishers:

  • Nebulasteam Gun finisher:
    • Funky Drive (ファンキードライブ Fankī Doraibu): Engine Bro's channels the power of a Gear and performs a powerful blast attack.
      • Gear Engine:
      • Gear Remocon:
    • Funky Attack (ファンキーアタック Fankī Atakku) Engine Bro's channels the powers of a Fullbottle and performs a powerful blast attack.
  • Nebulasteam Rifle finisher:
    • Funky Shot (ファンキーショット Fankī Shotto): Engine Bro's channels the power of a Gear or Fullbottle and performs a powerful blast attack.
      • Gear Engine: Engine Bro's shoots an energy-like engine bolt at the enemy.
      • Gear Remocon:

Appearances: ROGUE, Build Episodes 23-26, 29-30, 32, 37-38




  • Steam Blade - Standard sidearm weapon. Can combine with the Nebulasteam Gun to form the Nebulasteam Rifle. Shared with Remocon Bro's.

Behind the Scenes


Rai is portrayed by Yuudai Nasuda (奈須田 雄大 Nasuda Yūdai). As a teenager, he is portrayed by Taiga Watanabe (渡辺 虎雅 Watanabe Taiga), who previously played a baby in Kamen Rider Den-O and also the son of suit actor Jun Watanabe.

As Engine Bro's, his suit actors were Keisuke Azuma (東慶介 Azuma Keisuke) and the late Daichi Nobe (野邉 大地 Nobe Daichi).


The Kanji that makes up Rai's first name (雷) translates to "thunder". This also explains the meaning behind his prideful and boastful personality: "Loud like thunder".



Sento Kiryu - Ryuga Banjo - Kazumi Sawatari - Gentoku Himuro - Evolto - Nariaki Utsumi - Shinobu Katsuragi - Kengo Ino - Killbus - Keiji Uraga
Transformation Gear
Fullbottles - Build Driver - Transteam Gun - (Great) Cross-Z Dragon - Sclashjellies - Sclash Driver - Hazard Trigger - Nebulasteam Gun - Cross-Z Magma Knuckle - Evol-Driver - 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
Prime Ministers: Taizan Himuro (Touto) - Yoshiko Tajimi (Hokuto) - Masakuni Mido (Seito)
Namba Heavy Industries Ltd.: Juzaburo Namba - Nariaki Utsumi - Guardian
Hell Bro's: Fu Washio - Rai Washio
Aliens: Vernage
Downfall: Keiji Uraga - Simon Marcus
Gentoku Himuro - Evolto - Nariaki Utsumi - Takumi Katsuragi - Shingo Kuwata - Eita Kawai
Touto: Needle Smash - Strong Smash - Burn Smash - Flying Smash - Mirage Smash - Square Smash - Press Smash - Ice Smash - Stretch Smash
Hokuto: Castle Hard Smash - Stag Hard Smash - Owl Hard Smash
Kaiser: Kaisei Mogami (World of Ex-Aid)
Kengo Ino - Ryoka Saiga - Mitsuomi Gobara - Evolto - Killbus