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]

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

"I didn't do this to save you...but to protect...the Lost Bottle."
―Utsumi final words after shielding Gentoku and Sawa from Evol's Steam blade.[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 was 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, Utsumi was converted into a cyborg in order to save his life.Zero Degree Flames At some point, he upgraded the Kaiser System created by Kaisei Mogami and tested its Hell Bro's (ヘルブロス Heru Burosu) transformation.

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 with 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. Although this was all a ruse to avenge 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 barely survived the fall and was pulled out of the river by Blood Stalk, and later on turned into a cyborg before being placed in the science division of Namba Heavy Industries. The night of Kamen Rider Grease's arrival, Gentoku Himuro arrived at the Industries, waiting to talk to Juzaburo Namba until Utsumi approached him. 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.

Utsumi's insane laughing

Utsumi goes insane and preparing break his benefactor's walking cane.

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

Acting on behalf of Evolto, Utsumi appeared before Gentoku and Kazumi, whom had been held in captivity by the Blood Tribe. Utsumi returned their Sclash Drivers, allowing them to transform and escape, but not before making them grovel for his assistance. Kamen Rider Build: Be The One


During Team Build's final battle against Evolto, Utsumi appears before Gentoku after he faced the clones of Engine and Remocon Bros. Transforming into MadRogue, Utsumi unexpectedly attacks Engine and Remocon Bros, showing his ruse against Evolto. Gentoku claims that he's indeed 'mad' and Utsumi calmly said that he's still a Namba Children at heart. They then form an alliance against Hell Bros.

Sawa later arrives with Pandora Box and gives MadRogue the Shark and Bike Fullbottles. MadRogue states that he implants a weakness against the clones, and using the Shark and Bike Fullbottles can neutralize their attacks, which they used to defeat the Hell Bros clone. However, Evol Cobra then arrives to collect the Purified Hammer Lost Fullbottle that he inject earlier to the Hell Bros clone.

Evol easily defeats both Rogues, until MadRogue activates the data he had collected from Evolto's Evol-Driver, dubbing them as 'Phases'. MadRogue then attacks Evol with super speed after he activates Phase 3, thus giving Evol a Hard time. But, after activating Phase 4, MadRogue stops all of sudden and receive a direct hit from Evol's punch, canceling his transformation.

Evol then explained that Utsumi could handle Evol's power since Utsumi wasn't totally human anymore. After Gentoku had shot him, Evolto turned him into a cyborg. Apparently, Phase 4 overloaded Utsumi's systems, hence why he suddenly stops. Evol then was about to kill both Gentoku and Sawa to obtain the Hammer Lost Fullbottle, but Utsumi manages to shield Evol's Steam Blade with his body, thus deactivating him as Evol throws Utsumi’s corpse away. Gentoku then successfully flees with Sawa, saving the Lost Fullbottle. His last words before dying implied that he was yet intended to save the world as he said "All for Namba" Zero Degree Flames

New World

New Utsumi

Utsumi, working at the Namba Machine Workshop.

After Sento defeats Evolto for good, the new world had been successfully created. This world’s version of Utsumi is working at the Namba Machine Workshop and is shown making a steel rebar. For some reason, Utsumi deems that the rebar is not up to standard and intends to break it using his knees, which he failed. The Tomorrow Build Will Create


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.

After Namba was killed by Evolto, Utsumi eventually was seemingly driven insane and chose to pledge his loyalty to Evolto. In addition, Gentoku himself was implied to have 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.

However, it was revealed that Utsumi's maniacal behaviour was a ruse to avenge Juzarubo Namba, doing so by collecting an Evol Driver and examining Evolto's attacks and physiology to come up with countermeasures, revealing Utsumi as a proficient liar and mastermind. Gentoku even states that Utsumi is really 'Mad' as he looks.

Powers and Abilities

  • 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.
  • Cyborg Physiology: In order to save his life after he was shot by Gentoku and fell off the bridge, Utsumi was turned into a cyborg by Namba Industries. The extent of the abilities this grants him are unknown, but it may be what makes him able to emulate Evol's Phases. However, attempting to use Phase 4 caused him to overload. It may also be possible that Utsumi's cyborg nature is what allows him to use an Evol-Driver.
    • High Hazard Level 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. When posessing Utsumi's body and fighting against the Kamen Riders, Evolto implied that he had modified Utsumi's Evol-Driver somehow so that it would be suitable for the human body. This hints that Utsumi's Hazard Level may either be artificially or temporarily raised, or that his Evol-Driver requires a lower Hazard Level.


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 t.
  • Kicking Power: 50.6 t.
  • 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 t.
  • Kicking Power: 50.8 t.
  • 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 has higher punching and kicking power 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.

MadRogue's main feature is the explosion-proof CyBat Armor (サイバットアーマー Saibatto Āmā) that allows his gear to continue functioning in battle. 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. 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.

MadRogue's wings

MadRogue's wings

After inputting Evol's data into his Driver, Utsumi was able to mimic his abilities up to Phase 3. In Phase 3 he demonstrated Evol's super speed and energy covered punches, which allowed him to fight on par with Evol himself. Utsumi also attempted to use Phase 4, but his cybernetics overloaded before he was able to do so.

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 six 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.
      • MadRogue performs a low kick covered in purple energy to an enemy on the ground.
      • MadRogue fires a steam projectile covered in purple energy from the Nebulasteam Rifle.
      • MadRogues unleashes two energy slashes from the Steam Blade that travel through the air and follows them up with sustained fire from the Nebulasteam Gun.
      • After replacing the Engine Fullbottle with the Bike Fullbotle and initiating the Evoltic Attack, MadRogue summons the Machine Builder, which redirects the enemy's attacks by binding them to it's front wheel before ramming into the enemy.
  • Evol Driver + Kaizoku 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, 42, 44-45, 47



  • 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.



Nanba Heavy Industries/Faust

  • Juzaburo Namba: Utsumi shows to be very loyal to him, even after Evolto kills Namba.

Enemies/Team Build

  • Sento Kiryu/Katsuragi Takumi: Both are scientists but were used by Gentoku to start the war.
  • Ryuga Banjo: An enemy.
  • Kazumi Sawatari: Had victimized his friends in Hokuto forcing him to give Pandora's Box in exchange for their freedom.
  • Gentoku Himuro: Formerly his superior in Touto, Gentoku shot Utsumi as a way of covering his tracks. But returned revealed working for Nanba until his chairman's/president's death at Evolto's hands. Gentoku was responsible for Utsumi's desension to madness as MadRogue.
  • Misora Isurugi: Grabbed the Evol Driver from her, while she was distracted seeing her father as Blood Stalk.
  • Sawa Takigawa: She and Utsumi were from the Nanba Children. But despite her joining Team Build permanently, he called Sawa by the phone letting her know of his plans in destroying Evolto from the inside.


  • Evolto: Served under him gaining the power to become Kamen Rider MadRogue, until revealing his plan to destroy him from the inside.
  • Shinobu Katsuragi: Worked alongside him with Evolto until his true agenda was revealed.

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).


The ending scene in episode 38, where Utsumi snapped Namba's cane after feigning insanity has been made into a meme which involves parodying said scene into various situations. In the Japanese fandom, this is labelled under the Twitter hashtag Nariaki Utsumi Darn Collaboration Grand Prix (内海成彰クソコラグランプリ Utsumi Nariaki Kuso Kora Guranpuri). Kouhei Takeda and Eiji Akaso has also recreated this scene on Yukari Taki's Twitter page, and Instagram story.


Utsumi insanity

Sento's depiction of "cyborg Utsumi".

  • Utsumi's stoic personality for most of the series has led to a few occasions where Sento/Katsuragi jokes about Utsumi being a "cyborg" in the opening recap narrations of episodes 19 and 39. This is an ironic foreshadowing to episode 47 where it was revealed that he was actually turned into a cyborg.
  • Like Night Rogue, MadRogue initially appears with a black undersuit which inexplicably changes to brown in later appearances.
Mad Rogue's Snap Ride Builder

MadRogue with a Snap Ride Builder



Sento Kiryu - Ryuga Banjo - Kazumi Sawatari - Gentoku Himuro - Evolto - Nariaki Utsumi - Shinobu Katsuragi - Kengo Ino - Killbas
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
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 - Build Annihilation Plan
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
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 Gohara - Evolto - Killbas