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Anything for Namba Industries!
~ Rai and his brother's chant.

Rai Washio is a Namba child working as a supersoldier of the Seito government and a supporting antagonist in Kamen Rider Build.

He was portrayed by Yuudai Nasuda.



Rai and his older brother Fu were raised by Namba Heavy Industries as Namba Children, being indoctrinated and undergoing brutal training to become soldiers.


After Kiba defeated some Seito Guardians as Owl Hazard Smash, Rai and Fu showed up and quickly dispatched the Hokuto Crow as Remocon and Engine Bro's. They then tell Grease to become a Seito weapon if he wants Kiba to live.

After torturing Kiba for a bit, Kazumi and Akaba appear and confront the Washio brothers and free their comrade. Grease and Akaba manage to escape with Kiba, but Grease later suffers a shot from Fu's Nebula Steam Rifle. Rai's brother attempts to kill Grease, but Kiba takes the attack. Akaba and Kazumi then escape to Sky Road to meet up with Sento and Ryuga.

Rai and his brother pursue them and are fought by Sento and Ryuga as Build Rabbit Tank Hazard and Cross-Z Charge respectively. However, the battle is interrupted when Kamen Rider Rogue appears.

During Seito's forces incursion on the Touto government office, Rai and his brother provided cover for Rogue as he went to acquire the Pandora Box. The Washio brothers fought Kamen Riders, Cross-Z Charge, Grease and Build, though Build managed to catch up with Rogue.

The Washio brothers later represented Seito alongside Rogue in a three-stage Proxy Battle with Touto. Rai was defeated by Grease in the first round. During Fu's fight with Cross-Z Charge in the second round, Fu got Ryuga to lower his guard by claiming him his brother would be executed if he failed, using Ryuga's hesitation as an opportunity to knock him out of the battle. Rai then appeared unharmed to gloat with his brother.

Engine Bro's and Remocon Bro's were later sent by Namba to keep an eye on Evolt as he met with Ryuga and Kazumi Sawatari to exchange the Pandora Box. After Evolt revealed he had no intention of holding up his end of the bargain (freeing Sento), he sent the two Kaisers to fight Kamen Rider Grease, not believing him to be worthy of challenging him. Engine Bro's was defeated along with his brother by Kamen Rider Rogue when he arrived, prompting Evolt to enter the fight himself.

Rai and his brother were later sent by Namba to accompany Evolt when he went to meet with Ryuga and Kazumi to claim the Pandora Box from them. After revealing he has no intention of holding up his side of the bargain, Evolt sends the two Kaisers to attack them, not deeming them worthy of being fought by himself. Kazumi transforms into Kamen Rider Grease and engages them, though whenever he obtained the upper hand, Evolt would interfere and allow the Kaisers to gain the advantage. However, Kamen Rider Rogue then appears and defeats both Engine Bro's and Remocon Bro's before turning his attention to Evolt.


After assuming his Black Hole form, Evolt declared to Namba that he would supplant him as the ruler of Seito, though Namba refused to give up his power and go along with Evolt's plans. In order to match up to Evolt's powers, Rai and his brother were dosed with more Nebula Gas by Nariaki Utsumi, though this had the side affect of killing them should they revert out of their transformations. As Remocon Bro's, Fu accomanied his brother, Utsumi and a squad of Hard Guardians to confront Evolt. Unfazed by Namba's refusal to comply, Evolt transformed into Kamen Rider Evol Black Hole and turned the battlefield to a barren valley for them to fight in.

After Evol destroyed the Hard Guardians, Remocon and Engine Bro's were sent in to fight him, though they fared little better against the powerful Rider. However, backup soon arrived in the form of the heroic Kamen Riders, though even with their combined power, they were unable to lay a scratch on Evol. Evol eventually decided to finish everyone off and used his Black Hole finisher to take out Rai Washio. Before dying, Rai tossed Fu his Fullbottle for him to transform into Hell Bro's with and bid his brother farewell.


Engine Bro's

KRBu-Engine Bros.png


  • Height: 202.0cm
  • Weight: 103.5kg
  • Punching power: 30.5t
  • Kicking power: 37.2t
  • Jumping power: 48.6m (one jump)
  • Running power: 1.7 seconds (100m)
  • Special move: Funky Drive


  • Engine Bro's Head - The head of the Engine Bro's.
    • EB Side Blade - Engine Bro's's data collection device. It is possible to aggregate battle data in real time and accurately grasp the abilities of yourself and the enemy. It also manages the condition of the whole body, and if there is a damaged part, it automatically performs emergency repair.
    • Dusk Seeker Eye - Engine Bro's's visual sensor. It is a high-sensitivity sensor with a night-vision function, and can instantly detect moving object reactions and heat source reactions. It can also detect chemicals in the air and look for traces of enemies.
    • Air Face Duct - Engine Bro's's intake and exhaust system. It has the role of removing harmful substances when taking in the surrounding air inside. It is also possible to discharge toxic gas.
    • Engine Dark Visor - Protective parts attached to Engine Bro's's face. The shock-resistant frame is stretched around, and it demonstrates high defense performance against physical attacks.
    • Grudge Signal - Engine Bro's's output regulator. When the angry emotions of the transformant exceed a certain level, the chest strengthening device "Nebula Generator" is activated at high speed, providing combat power that is difficult to control.
    • EB Face Guard - A protective device that protects Engine Bro's's head. It is possible to minimize damage by emitting waves that attenuate the enemy's energy attack.
  • Gear Steam Shoulder - Armor that protects Engine Bro's's shoulders. Optimize the movement of the arm to improve the attack accuracy. It is also possible to disperse the appearance by spraying colored gas through the gaps in the armor.
  • Gear Torque Gauntlet - An attack device attached to Engine Bro's's arm. It is possible to generate and inject a gear-type energy cutter.
  • Dominate Gloves - Reinforced gloves that cover Engine Bro's's fist. It has a shape specialized for fighting attacks, and is good at continuous thrusting using a claw with a sharp fingertip.
  • Punishment Leg - Engine Bro's's legs. It has both power and speed, and is good at high-power knee kicks and continuous kicks.
  • Idron Shoes - Engine Bro's's battle shoes. He is good at lean, quiet and quick movements, and can approach behind without being noticed by the enemy. It is also possible to emit a special steam from your feet and create an afterimage to confuse the enemy.
  • Punishment Arm - Engine Bro's's arm. It has both power and speed, and is good at high-powered elbow strikes and continuous punches.
  • Cog Chest Armor - Robust armor that protects Engine Bro's's chest. Equipped with a device "Nebula Generator" that uses special steam to strengthen the fighting ability, it is possible to speed up all movements of itself for a certain period of time and increase the power of attacks.
  • EB Unlimited Suit - Engine Bro's's shock-resistant bodysuit. At the same time as protecting the transformant from combat damage, it is possible to release the physical limiter and bring out the hidden physical ability.
  • Metal Knee Bat - Armor that protects the knees of Engine Bro's. Optimize leg movements to improve exercise speed.


Rai Washio

Engine Bro's


           BUILD LOGO.png Villains

Night Rogue | Blood Stalk | Takumi Katsuragi | Nariaki Utsumi | Shingo Kuwata | Eita Kawai | Masahiro Nabeshima | Norio Matsui | Yoshikazu Takahashi | Shinobu Katsuragi | Faust Guardians

Yoshiko Tajimi | Blood Stalk | Kazumi Sawatari | Hokuto Three Crows | Akaba | Aoba | Kiba | Massugu Ubukata | Hokuto Guardians

Masakuni Mido | Kamen Rider Rogue | Fu Washio | Rai Washio | Seito Guardians | Hard Guardians

Namba Heavy Industries Ltd.
Juzaburo Namba | Nariaki Utsumi | Fu Washio | Rai Washio | Sawa Takigawa | Kaisei Mogami | Guardians | Hard Guardians

Blood Tribe
Killbus | Evolt | Kengo Ino | Ryoka Saiga | Mitsuomi Gohara

Needle Smash | Strong Smash | Burn Smash | Flying Smash | Press Smash | Ice Smash | Stretch Smash | Fang Smash

Simon Marcus | Keiji Uraga | Phantom Crushers | Guardians | Hard Guardians