|“||Anything for Namba Industries!||„|
|~ Fu Washio's chant along with his brother.|
He was portrayed by Osamu Adachi.
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 represented Seito 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.
Fu 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 Remocon Bro's and Engine 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, Fu 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 Rai died, he tossed Fu his Fullbottle for him to transform into Hell Bro's with. Assuming Hell Bro's, Fu charged at Evol in a fierce attack that amounted to nothing. Before Evol could kill him however, he was saved by Cross-Z Magma, who then tried fighting off Evol with little success. Forced out of his transformation, Ryuga was about to be finished off by Evolt when Hell Bro's shoved him out of the way and took brunt of the attack instead. His transformation canceled by the attack, Fu stated it was nice to fight for somebody else for a change and that he should tell Rai about it before fading away.