This article is about a/an rider in Kamen Rider Build.

―Night Rogue's transformation catchphrase.[src]

―Hell Bro's transformation catchphrase.[src]

"Where did I go wrong? I just...wanted to live a normal life...laughing at silly things...and crying with emotion. Don't become like me. Sento Kiryu."
―Utsumi's confession about his ideals his life[src]

"If that's the case, then there's only one answer! I swear my loyalty to you!"
―Utsumi goes insane after the destruction of Namba and swears allegiance to Evolto.[src]

Nariaki Utsumi (内海 成彰 Utsumi Nariaki) was the assistant of Gentoku Himuro at the Touto Institute of Advanced Matter Physics. He was also an aide to the Prime Minister of Touto and a former member of Faust.

He is later used as a decoy in order to hide the true identity of Night Rogue (ナイトローグ Naito Rōgu) during Touto's operation against Faust, before being gunned down by Gentoku himself and falling off a bridge into a river.

Saved by Evolto and revealed to be one of the Namba Children raised with undying loyalty to Juzaburo Namba, he upgraded the Kaiser System created by Kaisei Mogami and was able to transform into the Hell Bro's (ヘルブロス Heru Burosu).

He becomes Kamen Rider MadRogue (仮面ライダーマッドローグ Kamen Raidā MaddoRōgu)[1] using the Evol-Driver and the Bat and Engine Fullbottles when he is offered the Driver by Evolto, initially rejecting him but devoting his loyalty to Evolto when he kills Namba.

Character History

Utsumi is first seen reporting to Gentoku about Sento's application for a job at the Touto Institute of Advanced Matter Physics, noting that Sento had passed the entrance test with a perfect score.

Utsumi is Sento's direct superior at the Institute, reporting directly to the Prime Minister of Touto, Taizan Himuro, while at the same time also secretly assisting Gentoku/Night Rogue within Faust. He was one of the first present witnessing Taizan's collapse, after the Pandora Box was stolen from the Institute. The Box was later hidden within a secret basement at one of Namba Heavy Industries' laboratories.

Faust's Pandora Box Plan

Shortly after the emergence of a second Kamen Rider, Utsumi was called upon by Juzaburo Namba for a favor. Later, as he watched Sento return to work despite it being a day off for all lab staff, Utsumi decided to reveal the location of the Box's hidden location to Sento. Though, the Box ended up being reclaimed by Blood Stalk, and Utsumi was eventually forced to cooperate with Namba in his plan: to assume the identity of Night Rogue as a decoy in a staged operation by Touto to supposedly take down Faust. Due to Build's intervention, Utsumi was seemingly exposed as Faust's creator, though Build suspected that something was amiss.

A scientist's misery

Utsumi just before his "death".

Chased by Build to a bridge above a river, Utsumi, at his wits' end, confessed his inner troubles as a scientist. Revealing that he already knew that Build was Sento for a long time already, Utsumi urged Sento to not land into the same fate as his, and warned him to 'turn back' when he still have the time before he was shot in the shoulder by Gentoku, causing Utsumi to fall into the river below to his apparent demise.


LTNS Himuro

Utsumi working at Namba Heavy Industries.

"It's been a while...Himuro."
―Utsumi's first word upon meeting a former superior[src]

However, he survived and was pulled out of the river by Blood Stalk. He now works at Namba Heavy Industries and greeted his former superior, who was waiting for Juzaburo Namba. The Golden Soldier

Utsumi was approached by Gentoku, whom had been banished from Touto on his father's orders. Utsumi accepted Gentoku's request to be made into a Kamen Rider but not before taking pleasure in making him swallow his pride and beg for it. A Man Called Rogue

On Stalk's orders, Utsumi went to Nascita where Sento Kiryu was surprised to see him alive as well as being able to make vastly superior coffee to Soichi Isurugi. Taking him underground, Utsumi revealed his intent to continue Sento's training to master the new Fullbottles left to him by Stalk in preparation for his deciding match against Kamen Rider Grease. Though Sento performed efficiently against simulated Smash Hazards with basic Best Matches, Utsumi pointed out that he would have to use the Hazard Trigger to defeat Grease. Sento understood this, and had already designed blueprints for a device which would cancel his transformation, if he went berserk. But it needed data of his Hazard Form's performance to complete it, to which Utsumi obliged by transforming into Night Rogue once more, using his self-made Transteam Gun from Gentoku's Blueprint. Though he overwhelmed by SmaphoWolf Hazard as Build gone berserk, Utsumi was able to complete the dangerous procedure by using holographic Smashes to distract the rampaging Build, allowing him to forcefully pull out the Hazard Trigger and cancel Sento's transformation. With the data he needed collected, Sento was called away to intercept an attack on a Fullbottle facility. First Chapter

Working on behalf of Namba, Utsumi updated the Kaiser System originally developed by the late Kaisei Mogami to create Remocon and Engine Bro's, which would be used by soldiers of Seito, Namba's prefered choice to inherit Japan. Utsumi was given the personal thanks of Seito's Prime Minister Masakuni Mido. The Phantom of the West

Teaming Up With Evolto

As Evolto reaches the final phase of his plan (Phase 4/Black Hole), he openly declares to Namba that he'll now rule the world. Knowing this, Utsumi prepares for all-out war against Evolto, such as injecting Nebula Gas into the Washio brothers and even contacting his former boss to temporarily make an alliance.

However, Evolto was too strong to handle, even when Build, Rogue, Cross-Z and Remocon Bros teamed up. After Fu and Rai Washio, and Namba himself are killed, Evolto gives his last chance to Utsumi, making him choose whether he would fight to avenge Namba or fight for him.

At this point, Utsumi finally goes insane. He renounced his connection with Namba by breaking his benefactor's walking cane and joining Evolto who, in return, gave Utsumi the second Evol Driver. Using the Bat and Engine Fullbottles, he became a Kamen Rider, whom Evolto christened as MadRogue.Mad World


Not much known about Utsumi's personality other than being a loyal assistant to Gentoku, even when his superior is revealed to be manipulating the Touto government from behind the scenes as the leader of Faust. He is shown smirking whenever Gentoku, as Night Rogue, fights with Blood Stalk.

It is later revealed that there is also a hidden depth to his personality, as Utsumi admits to Sento that they have a lot in common whenever they are trapped in difficult situations. He admits that he wanted to live a simple life as a scientist but had lost his way as time passed, and warned Sento not to fall down the same path as him as a fellow scientist.

After being saved by Stalk and working with Namba, Utsumi seems to be more open-minded. He also faintly smiles after he finished the battle simulation with Sento. However, Utsumi proves to be more maniacal and ruthless, as demonstrated when Gentoku, after being exiled, asked Utsumi to make him a Kamen Rider. He asks Gentoku to kneel, and after he does so, Utsumi steps on Gentoku's hand, reveling in sadistic laughter as he took his revenge for Gentoku's failed attempt to kill him.

Despite being employed under Juzaburo's (and by proxy, Stalk's) orders, Utsumi is unnerved by Stalk's murder of Mido and Juzaburo going overboard in his ambitions of creating his Namba Empire with the power of the Pandora Tower. However, Utsumi has no qualms resorting to underhanded methods himself. In addition of taking Kazumi Sawatari's farmers hostage in order to blackmail him into betraying Touto, he also grabbed Misora and threw her to the ground in order to take the Evol-Driver from her hands. He also eagerly takes advantage on the chip implanted in Gentoku's body. Utsumi is quite cowardly, and his ego is quickly inflated the second he gets an upper hand. Utsumi was completely terrified when Gentoku attempted to rebel, but quickly regained his confidence after Gentoku was immobilized by his killswitch and violently attacked the unarmed Gentoku.

Utsumi insanity

Utsumi, having gone insane.

After Namba was killed by Evolto, Utsumi eventually was driven insane and chose to pledge his loyalty to Evolto. In addition, Gentoku himself had a part in Utsumi's aforementioned descent into madness due to the fact that him shooting the latter under the bridge was the reason behind Utsumi's currently maniacal behavior.

Powers and Abilities

  • Hazard Level 5 Physiology: It is implied that Nariaki seems to have a high Hazard Level, due to his capability of using the Transteam Gun. Night Rogue Chapter This is later confirmed, as he is capable of using the Evol-Driver, which requires a minimum of Hazard Level 5, a feat no ordinary human can accomplish.
  • Genius-Level Intellect: Since Utsumi had worked for the Touto Institute, he possessed a certain level of intellect and this allows him to elevate to the rank of Gentoku's assistant. Because of this, Gentoku had speculated that Utsumi had a hand in the creation of Hokuto's Sclash Driver for Kamen Rider Grease, something which Sento Kiryu also suspected; this is later confirmed after Seito invades Hokuto, when it is revealed that Utsumi has built and upgraded another Sclash Driver for use by Kamen Rider Rogue, as well as duplicating Kaisei Mogami's Nebulasteam Gun for use by the Hell Bro's, all as part of Namba Heavy Industry's partnership with Seito. Utsumi also has access to data on some of Build's forms, including the Hazard and RabbitRabbit Forms, using them to Namba's advantage.


Night Rogue
KRBu-Night Rogue

Night Rogue

Night Rogue visor view

Night Rogue analyzing Build's SmaphoWolf Hazard Form.

"Bat! Mistmatch! Bat...Ba-Bat... Fire!"
―Transformation announcement[src]
  • Height: 197.5 cm.
  • Weight: 103.0 kg.

Ability Perimeters:

  • Punching power: 17.2 t.
  • Kicking power: 20.5 t.
  • Maximum jump height: 49.0 m.
  • Maximum running speed: 100 m. per 4.1 sec.

Like Blood Stalk, Night Rogue's form is accessed with the Transteam Gun and the Bat Fullbottle.

Unlike Build, Night Rogue's Ability Perimeters are not spread out between his arms and legs. While Night Rogue gets power from only one Fullbottle, he's much stronger than Build's Trial Forms and his stats even surpass some of Build's Best Matches.

Utsumi's transformation into Night Rogue allows him to last for a good while against Build's Hazard Forms, at most before Build starts losing control. Utsumi, as Night Rogue, can also use his visor to analyze Build's stats.

Utsumi originally transformed into Night Rogue to act as Gentoku's decoy in order to keep his identity a secret. Later, he would use this form several more times in order to collect data on Sento while Gentoku was being experimented on in order to become Kamen Rider Rogue.

Appearances: Build Episode 12, Raising the Hazard Level ~7 Best Matches~ ("First Chapter", "Final Chapter")

Hell Bro's
KRBu-Hell Bros

Hell Bro's

"Gear Engine! Gear Remocon! Funky Match! Fever! (Rhythmic beeping, engine revving) Perfect!"
―Transformation announcement[src]


  • Height: 202.0 cm
  • Weight: 108.0 kg

Ability Perimeters:

  • Punching Power: 41.6 tons
  • Kicking Power: 50.6 tons
  • Maximum Jump Height: 64.8 m
  • Maximum Running Speed: 100 m. per 1.4 sec.

Hell Bro's is the fusion of the Kaisers Engine Bro's and Remocon Bro's, transformed into by inserting the Gear Engine or Gear Remocon into the Nebulasteam Gun, then removing it and inserting the other.

This form is exclusive to Kamen Rider Build: Raising the Hazard Level ~7 Best Matches~: "Next Chapter".

Kamen Rider MadRogue

Kamen Rider MadRogue

"Koumori! Hatsudouki! Evol Match! Are you ready? BatEngine! Fuhahahaha!"
―Transformation announcement[src]


  • Height: 196.0 cm
  • Weight: 105.8 kg

Ability Perimeters:

  • Punching Power: 43.5 tons
  • Kicking Power: 50.8 tons
  • Maximum Jump Height: 73.3 m
  • Maximum Running Speed: 100 m. per 1.3 sec.

Utsumi transforms into Kamen Rider MadRogue by inserting the Bat and Engine Fullbottles into the Evol-Driver and turning the lever.

As MadRogue, Utsumi becomes a force to be reckoned with, as he is more powerful than Build's Rabbit Rabbit Form while also having a slightly lower running speed and jump height than its base perimeters. He is able to overwhelm Rogue and Grease in every area, but is also easily outclassed by all of Evol's forms and Cross-Z Magma.

His main feature is the explosion-proof CyBat Armor (サイバットアーマー Saibatto Āmā) that allows MadRogue's gear to continue functioning in battle even if his engine-like features blow up. His chest is equipped with the MR Steam Generator (MRスチームジェネレーター Emu Aru Suchīmu Jenerētā) that boosts his capabilities through a specialized steam and allows a temporary boost in speed and energy attacks. For aerial combat, MadRogue can deploy a pair of Mad Night Flyers (マッドナイトフライヤー Maddo Naito Furaiyā) from his back.[2] Through his MadRogue Head (マッドローグヘッド MaddoRōgu Heddo), he can utilize the Metal Bat Blade (メタルバットブレード Metaru Batto Burēdo) to establish a link with Hard Guardian and Clone Smash units.[3]

MadRogue wields the Nebulasteam Gun and Transteam Gun as his personal weapons and the Steam Blade as his sidearm. He is also able to wield any of Build's weapons if he inserts the corresponding Fullbottle into the Evol-Driver along with the Rider Evolbottle.

This form has two finisher:

  • Evol Driver Finishers:
    • Evoltic Attack (エボルテックアタック Eborutekku Atakku): This finisher has two variations:
      • MadRogue flies into the air with the Mad Night Flyers and rams into the enemy.
      • MadRouge leaps into the air and sprouts the Mad Night Flyers before delivering a flying dropkick to the enemy.
  • Evol Driver + Kaizuko Hassyar Finisher:
    • Pirate Finish/Kaizoku Densya: MadRogue inserts the Kaizoku Fullbottle and Rider System EvolBottle into the Evol Driver and turns the crank, summoning the Kaizoku Hassyar. He then charges the weapon by pulling the arrow and holds it for a period of time before letting it go. The weapon then fires a green and azure energy train that rams into the enemy several times.

Appearances: Build Episodes 38-40



  • Transteam Gun - Night Rogue's transformation device and personal weapon
  • Fullbottles - Night Rogue and MadRogue's transformation trinkets
  • Nebulasteam Gun - Hell Bro's transformation device and MadRogue's personal weapon
  • Gears - Hell Bro's transformation trinkets
  • Evol-Driver - MadRogue's transformation device


  • Steam Blade - Standard sidearm weapon. Can combine with the Transteam Gun to form the Steam Rifle or the Nebulasteam Gun to form the Nebulasteam Rifle.
  • Kaizoku Hassyar - MadRogue's weapon granted by the Kaizoku Fullbottle.


Behind the Scenes


Nariaki Utsumi is portrayed by Yuki Ochi (越智友己 Ochi Yūki). As Night Rogue, his suit actor is Jun Watanabe (渡辺淳 Watanabe Jun). As Kamen Rider MadRogue, his suit actor is Yuji Nakata (中田 裕士 Nakata Yūji).


Mad Rogue's Snap Ride Builder

Mad Rogue with a Snap Ride Builder

  • In Ganbarizing, Mad Rogue has a Snap Ride Builder appear around him when he transforms. In Build proper, there is no Snap Ride Builder.