Fu Washio

Fu Washio is one of Namba children and a supersoldier of the Seito government. He is an antagonist in Kamen Rider Build.

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

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

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

Fu 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, Fu 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 representedSeito alongside Rogue in a three-stage Proxy Battle with Touto. After Rai was defeated by Grease in the first round, Fu used his Gear Engine and his own Gear Remocon to transform into the Hell Bro's. Facing Cross-Z Charge in the second round, Fu was surprised to find his power matched by Cross-Z Charge. However, Fu managed to trick Ryuga into letting down his guard by telling him his brother would be executed if he failed. After knocking Ryuga out of the battle, Rai appeared unharmed to gloat with his brother.