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This article is about a/an villain in Kamen Rider Build.
Soichi Isurugi
Soichi Isurugi
Blood Stalk
Gender: Male
Series: Kamen Rider Build
Motif: Cobra, Blood, Steam Engine (Default Form)
Robot (Union State Form)
Villain Type: Leader, Anti-Villain
Affiliation: Nascita
Homeworld: TBA
Height: 201.5 cm
Weight: 102.0 kg
First Appearance: That One with the Best Match
Last Appearance: TBA
Number of Episode
TBA (Build)
Full list of appearances
Actor: Yasuyuki Maekawa
Tetsuo Kanao (Voice as Blood Stalk)
Blood Stalk
Blood Stark

―Blood Stalk's transformation catchphrase.[src]

"I'm the game maker. I derive the best strategy by considering every possibility. Everything is going as planned."
―Blood Stalk's speech to Night Rogue[src]

Soichi Isurugi (石動 惣一 Isurugi Sōichi) is the father of Misora Isurugi, the owner of the café nascita and one of the main villains in Kamen Rider Build. Upon finding the amnesiac Sento Kiryu, he gave him a place to stay in the basement of nascita. He is also the one responsible for creating the Sky Wall Disaster and is the true identity of Blood Stalk (ブラッドスターク Buraddo Sutāku), a general of Faust who “killed” Takumi Katsuragi (later revealed to be actually Taro Satou and has his corpse disguised as Takumi) and framed Ryuga Banjou for the murder. Who Takes Off The Veil?


Ten years prior to the events of Build, Isurugi was an astronaut working with the Kiwami Project, discovering the Pandora Box on Mars. However finding the box would change his mentality, which he jokingly admitted that it "did a number on his mind". At the ceremony back on Earth, he rushed the security guards and applied his hand to the Pandora Box, causing the Sky Wall Disaster. After a series of later psychological attempts, Soichi was arrested and placed in a mental hospital, but he escaped about a month later. Around the same time he was admitted into the hospital, Misora Isurugi was also admitted as well due to the exposure of the box's affects and gained the ability to purify Fullbottles.

At some point he opened up a café called nascita in Touto.

Seven years later, he was appointed as a special consultant for the Pandora Box, while also covertly joining Faust in the process. Around the same time, Misora joined Faust to purify the Fullbottles for them, not knowing it was for evil purposes.

After Misora eventually found out about Faust's evil intentions, she lost her will to do so, so Soichi "saved" her and escaped with her back to the cafe, where Soichi convinced her to purify the bottles for good. He stole the Pandora Box panels from the Touto Institute of Advanced Matter Physics to ensure their confidence. From Faust, he took along a Build Driver and an unknown number of Fullbottles; upon his return, he plastered the panel into one of nascita's basement walls.

Sometime later, he confronted Takumi Katsuragi about him trying to quit Faust. At that time, Taro Satou had just arrived for his drug-testing job and was killed by Stalk. Knocking Katsuragi out, Stalk switches the two's faces and clothing, and leaves Taro Satou (with Takumi's appearance) there. He takes the out-cold Katsuragi (with Satou's appearance) and erased his memories before talking him back to Faust to experiment on him.

On September 5th, he brought the now-amnesiac Katsuragi to a small alleyway on a rainy day. While waiting for Katsuragi to wake up, he went to buy an umbrella before coming back to a awake Katsuragi. Soichi renames him Sento Kiryu and nurtured him into Kamen Rider Build. This was to ensure that as Build continues fighting more monsters, he'll find needs to purify more bottles by having Misora do so.

Isurugi, as Blood Stalk, made contact with Sento shortly after Sento defeated Masahiro Nabeshima as the Mirage Smash by stabbing him in the back with a venomous tentacle, leaving him stunned. Stalk then used a giant projection of a cobra to retrieve the incapacitated Nabeshima. Gentoku Himuro seems to be aware of Blood Stalk's activity. Borderline of Justice

Be the Stalk

Soichi about to Transform into Blood Stalk

The False Kamen Rider


Ten years ago, Soichi was known to be a kind and caring person, until he was exposed to the Pandora Box's energy, which changed his morality to the point where he became cruel and ruthless.

As the owner of Nascita, Soichi is an enthusiastic but laid back person who occasionally sprinkles his speech with Italian. When in panicked state, Soichi becomes careless, hidden behind his laid back demeanor is a secretive and somewhat manipulative man, albeit restrained by his morality. Due to his exposure to the Pandora Box, Soichi has an unconscious urge to act impulsively, explaining why he caused the Skywall Disaster.

"Why didn't you finish him off... Stalk?"
"I'm the game maker. I derive the best strategy by considering every possibility. Everything is going as planned.
―Blood Stalk to Night Rogue[src]

"Have you lost your mind?"
"I told you before. Faust isn't yours!
―Blood Stalk's disregard for Night Rogue's authority[src]

"With Kamen Rider Build defeating evil monsters...Misora was able to purify the Bottles, thinking she was doing it for justice. In other words, that was all you existed for. You were merely acting the hero of justice. You were just playing Kamen Rider."
―Blood Stalk unveiling his manipulative persona to Sento[src]

However, as Blood Stalk, he is a self-proclaimed strategist. He also seems to have a lot more of an unperturbed attitude compared to the more focused Gentoku, nonchalantly fooling around even when doing his job as a Faust enforcer. Such is seen when instead of directly engaging Build, he was casually laying back and letting the Square Smash do most of the fighting, until it was the right time for him to interfere by making the Smash grow. He also dislikes taking orders from anyone, preferring to do things his own way.

Soichi also viewed his battles with both Build and Banjou as an experiment to measure their Hazard Level. He was visibly entertained when both of them had a rise in their Levels and gave them hints in return. He isn't even bothered by opposing Gentoku temporarily to let them escape so he can see how strong they become.

Soichi can be cruel and ruthless if he wants to, making him not much different from Gentoku in regards to their aggression. He is more than willing to commit more heinous acts, such as killing several Touto guards using his venom, and changing Eita Kawai's face into that of Shingo Kuwata just to show he could. Like Gentoku, he views science and the Rider System as instruments for war.

Powers and Abilities


  • Computer Proficiency: Isurugi has some level of programming knowledge, as he was able to hack the GPS on a stolen motorcycle, and stolen Sclashjellies data from Sento's computer.
  • Altered Physiology: Being the first human to be exposed to the Pandora Box, Soichi has demonstrated numerous superhuman abilities since his return from Mars.
    • Matter Reshaping: Isurugi was able to manipulate a tablet computer into a rod shaped item that he used as a back scratcher.
    • Superhuman Agility: Isurugi was shown to be able to leap at a scale far beyond human capacity after his battle with Build's RabbitTank Sparkling Form.
    • Isurugi switching face

      Soichi modifying a victim's face.

      Identity Manipulation: Using a cloud of steam from his hand, he can make anyone's face look like anyone else's; the process seems painful to those who are awake to feel its effects. While the permanence of the change is yet unclear, certain individuals have been shown to retain their new identities for more than a year. Initially thought to be an ability of the Blood Stalk system, this power has since been revealed to be a power gained from Soichi's time on Mars.
    • Isurugi memories wipe out

      Soichi erasing Takumi Katsuragi's past memories.

      Memory Manipulation: Soichi has shown the ability to erase the memories of others with nothing more than a touch of his hand. Unlike the amnesia induced by Nebula Gas, Soichi's memory manipulation is shown to be complete, causing a total wipe of the person's previous identity. However, with time, some victims have shown to be able to recover partial memories, skills, or even the entirety of their past given proper circumstances.
    • Hazard Level 3+: As a user of Transteam Gun, it seems that Soichi has a high Hazard Level that allows him to use such device.Night Rogue Chapter As Stalk, Soichi mentions that his and Gentoku's Hazard Level are at the same level and would stay the same due to the Transteam System being incapable of rising them.
  • Dagger Proficiency: Although a very subtle example, Soichi is capable of throwing knives at a high precision rate.The Weaponry Hero

Blood Stalk

  • Venom Whips: On each wrist, he has extendable venomous tendrils that can shoot out and stab victims, injecting them with venom capable of either paralyzing, killing, or even disintegrating them.
  • Activation Command: As Guardians are in fact sleeper agents of Faust, Stalk can snap his fingers to activate their true programming into serving him.
  • Typhoportation: He can escape any situation by becoming a cloud of red smoke and flowing away.
Stalk Cobra attack

Stalk's cobra head attack

BS Snakes

Two giant Cobra projection.

  • Energy Cobra Projection: Through his suit, Stalk can create an energy cobra projection that is used to attack or kidnapping victims or even to make quick escape from enemy attack.
  • Guardian Merging: Blood Stalk can merge with multiple Guardians becoming a Union State Form to turn it into a red variant and pilot it himself.
  • Voice Changer: As mentioned by Takumi himself, Stalk's equipment has the ability to change its user's voice tone freely to hide their identity.
  • Enhanced Durability: The true purpose of the Blood Stalk system is to encourage the rise of Hazard Levels in the Nebula Gas victims, thus he is shown capable of accepting far greater punishments from either Build or Ryuga. Instead of showing pain or discomfort, Stalk is otherwise enjoying the beatings so long that his opponent's Hazard Level rises.
  • Hazard Level Measuring: Blood Stalk could measure current hazard level of Kamen Riders / Smashes by simply touching them


KRBu-Blood Stark

Blood Stalk

"Cobra! Mistmatch! Co-Cobra... Cobra... Fire!"
―Transformation announcement[src]
  • Height: 201.5 cm
  • Weight: 102.0 kg

Ability Perimeters:

  • Punching power: 19.0 t
  • Kicking power: 22.7 t
  • Maximum jump height: 40.0 m
  • Maximum running speed: 100 m. per 4.7 sec.

Similar to Night Rogue, Blood Stalk accesses his main form with the Transteam Gun and the Cobra Fullbottle.

His stats are not only stronger than most of Build's forms, but also surpass Night Rogue's with only speed being slightly lower than his. Stalk also possesses numerous abilities in this form, such as being able to utilize a tentacle to inject venom into a human and either paralyze or kill them. He can also materialize a giant translucent cobra out of thin air to capture and collect victims.

His skill with the Transteam System, coupled with his enhanced durability, has allowed him to survive multiple skirmishes with Build and Cross-Z, and defeat Night Rouge in a duel.

With the Steam Blade or the Steam Rifle, he can use the following attacks:

  • Elek Steam (エレキスチーム Ereki Suchīmu): Blood Stalk shoots electricity at the enemy.
  • Ice Steam (アイススチーム Aisu Suchīmu): Blood Stalk performs an icy slash at the enemy causing them to freeze.
  • Devil Steam (デビルスチーム Debiru Suchīmu): Blood Stalk fires a "steam" bullet which will home in on the target and inject them with a dose of Nebula Gas. When used on a human, the person will turn into a Smash; when used on a Smash, the Smash will grow to gigantic proportions and their host will lose all memories once freed.

Blood Stalk has 4 finishers:

  • Transtream Gun finishers:
    • Steam Break (スチームブレイク Suchīmu Bureiku): Blood Stalk channels the powers of a Faust Fullbottle and performs a powerful blast attack.
      • Cobra: Blood Stalk shoot a purple energy ball that detonates upon impact.
    • Steam Attack (スチームアタック Suchīmu Atakku): Blood Stalk channels the powers of a normal Fullbottle and performs a powerful blast attack.
  • Steam Rifle finishers:
    • Steam Shot (スチームショット Suchīmu Shotto): Blood Stalk channels the powers of a Faust Fullbottle and performs a powerful steam blast attack.
      • Cobra: Blood Stalk shoot a purple cobra energy blast that detonates upon impact.
    • Steam Attack (スチームアタック Suchīmu Atakku): Blood Stalk channels the powers of a normal Fullbottle and performs a powerful steam blast attack.
      • Rocket: Blood Stalk shoots a powerful blast attack that takes the form of a rocket. The rocket flies around the enemy before coming to the ground for an explosion.

Appearances: Build Episodes 3-14, 16-17, 19

Red Guardian Union (damaged)

Guardian (Union State), red version

When multiple Guardians are combining into their larger battle robot form, the Guardian (Union State) (ガーディアン(合体状態) Gādian (Gattai Jōtai)), Blood Stalk can jump into the mix to make it a red variant that he controls.

Appearances: Build Episode 10




  • Steam Blade - Standard sidearm weapon. Can combine with the Transteam Gun to form the Steam Rifle.

Behind the Scenes


Soichi is portrayed by Yasuyuki Maekawa (前川 泰之 Maekawa Yasuyuki). As Blood Stalk, his modified voice was voiced by Tetsuo Kanao (金尾 哲夫 Kanao Tetsuo), who previously voiced Namakelder in Happiness Charge Pretty Cure!. As Blood Stalk, his suit actor is Kazuya Okada (岡田 和也 Okada Kazuya).


The katakana "sutāku" (スターク) in his name is usually translated as "Stark".


  • Soichi has the habit of saying out "Objection!" (異議あり! Igiari!) before voicing his comments. The style and tone used as he delivers the phrase is reminiscent of the same iconic phrase from the Ace Attorney game series.
  • Being a proprietor of a café where the main hero works and/or frequents in their spare time brings to mind Tōbei Tachibana and Kiyojiro Bando.
  • Blood Stalk's cobra motif, along with Night Rogue's bat motif, is part of the recurring bat/cobra/spider trio in the Kamen Rider franchise, a tribute to the first two Shocker monsters as well as the first monster to be upgraded.
    • Stalk's personality is similar, if anything, to Takeshi Asakura/Kamen Rider Ouja, another villain who is also based on Cobra Man.
    • In addition,as Soichi, he also serves a comic relief character similar to that of Naoya Kaido and DJ Sagara, who possess a Snake motif.
    • Same as Night Rogue, Blood Stalk's transformation catchphrase, "Jōketsu" (蒸血), is also a homage to Space Sheriff GavanIcon-crosswiki and Space Sheriff ShaiderIcon-crosswiki's catchphrase ("Jouchaku" and "Shouketsu")
  • His personality of playing around and unpredictability, as well as his special interest in the protagonist, is shared with Parado from the previous series. In addition, Stalk has a habit going against Rogue's orders just like Parado's defiance against Kuroto.
  • Soichi Isurugi is the second double-agent character who possesses a monstrous identity and a secondary voice, the first being Kuniteru Emoto/Virgo/Tachibana from Kamen Rider Fourze.
  • Soichi plays a similar role to Sou Fueki/White Wizard/Wiseman from Kamen Rider Wizard. Both are introduced as benefactors to the main Rider at first before revealing their villainous agenda. Also, they are the fathers to one of the respective female protagonists.
  • He's similar to DJ Sagara from Kamen Rider Gaim, as he was initially a supporting character but is later revealed to be the mastermind behind everything, and is snake-themed.
    • An inversion of their backgrounds, while DJ Sagara wanted to encourage growth and improvement of all species across the universe, being a passive observer to the results, Soichi does so to improve the already powerful and only while they remain useful to him, becoming directly involved to make it happen.
  • As a hint to Stalk's true identity as Soichi, the collar on Blood Stalk's suit was modeled after the collar of a space suit.[1]
  • The CGI model of Blood Stalk's Energy Cobra is a reuse of part of Kamen Rider Ouja's Venosnaker.



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