|“||In the end, I have to entrust this to you, my son. I've failed as a father. Takumi... Have you grow taller again?||„|
|~ Shinobu's last words to Sento|
Shinobu Katsuragi is the second-in-command of Faust and a major antagonist of Kamen Rider Build. He seemly appeared as one of the two secondary antagonists in the final arc (alongside Nariaki Utsumi) at first, until it is proven to be false. He was originally a member of INSET, the husband of Kyoka Katsuragi and the father of Takumi Katsuragi.
Originally believed to be dead, it was revealed that Shinobu was not only working with Evolt on the Lost Bottles but also was the leading member of the Mars exploration group ten years ago, making Shinobu the one that is truly responsible for Evolt's actions and the subsequent Sky Wall Disaster. Shinobu was also in charge of examining Ryuga Banjo due to his extraterrestrial origins. He is later revealed to have his own Build Driver, which he uses to become another Kamen Rider Build. In reality, Shinobu was secretly plotting to betray and kill Evolt and was assisting his son all along.
He was portrayed by Joji Kokubo.
At the time of Project Prominence, Shinobu was the lead member of the Mars exploration group. After Evolt possessed Soichi Isurugi and caused the Sky Wall Disaster with the Pandora Box, all three of the emerging nations put the blame onto Shinobu. Shinobu then faked his suicide and, with assistance from Reika Kine, smuggled himself out of Touto on that same day.
Hiding out in a Faust base, Shinobu continued to work with Evolt, who had begun acting as Blood Stalk, throughout the next decade. He created Lost Bottles, man-made Fullbottles that would transform a human into a Smash, as well as causing them to be more aggressive and thus easier to control and manipulate, which would play a vital part in Evolt's endgame. During the initial years that Evolt was on Earth, Shinobu was tasked with repairing his Evol-Driver under Project Evol. However, the Driver was taken and hidden away by his son Takumi, where Sento would later find it and reluctantly return it to Evolt.
After Sento and his friends discovered that Shinobu was still alive and well, they started to investigate about him in spite of Sento's disbelief that his father is a villain. Unbeknowest to Sento, Shinobu was later resurfaced at a Faust hideout in Hokuto where he sided with Evolt while searching for the Lost Bottles, while stating that Evolt had become much more emotional.
Shinobu then questioned Evolt as to why he killed Shimizu, to which Evolt informed him that his ex-lab assistant was spilling too much about their plans. Shinobu stated that he was the last candidate they had to become a Lost Smash, but Evolt told him they could use the Kamen Riders. Shinobu noted that that was certainly possible, though that it might not work on Build due to his Genius Form. Evolt then tells him to figure out a way around that.
After Black Hole Evol destroyed the Touto Government Office and retreated along with Kamen Rider Mad Rogue, Shinobu showed up as Build NinninComic and ambushed Ryuga Banjou and Kazumi Sawatari before retreating.
Later, after Kamen Riders Build Genius Form and Rogue defeated Mad Rogue, Shinobu showed up again as Kamen Rider Build and attacked Sento and Gentoku, giving Utsumi cover to escape. Remarking that the Rider System wasn't built for "idealistic nonsense", the second Build reverted from his transformation, revealing himself as Shinobu Katsuragi.
Shinobu comments on how Sento / Takumi is the same despite his face being different before Evolt arrives and reveals that, not only are he and Shinobu working together, but that Shinobu manipulated both Sento and Ryuga into becoming Riders. As Evolt leaves with Utsumi, Shinobu transforms into Kamen Rider Build NinninComic and engages Kamen Riders Cross-Z Magma, Rogue and Grease while Sento stays back and contemplates his father's betrayal.
After Shinobu switches to HawkGatling form, Cross-Z Magma witnesses visions of Evolt destroying Mars and flies into a rage, fiercely attacking the second Build and beating him down. However, Sento, refusing to give up hope for his father, transforms into Kamen Rider Build Genius Form and dive kicks Cross-Z off Shinobu, knocking Ryuga out and allowing Shinobu to escape.
Completing the Black Pandora Panel
After Evolt kidnapped Misora Isurugi, Shinobu subjected her to a high level of Nebula Gas to transform her into CD Lost Smash. He later sends her out to confront Sento in an abandoned warehouse, with him soon joining the battle as well as Build RabbitTank. During the fight, Shinobu reveals that his motivations for working with Evolt are to complete the Black Pandora panel with the 10 Lost Bottles in order to unlock the door to a new world beyond the laws of physics as we know them. Sento then asks if he lied to himself and Kyoka just to accomplish this goal to which Shinobu confirms his statement before knocking him out of his transformation with a VolTech Finish. As Sento lies hopeless on the ground, Ryuga Banjou arrives and encourages him not to stop being a hero, giving Sento the courage to stand up and fight on.
Sento later manages to revert Misora's transformation by transferring the essence of Vernage within her into Ryuga, purifying another Lost Bottle and giving Ryuga an antibody against the cells of Evolt within him. Build Genius Form and Cross-Z Magma then engage Shinobu and beat him down, prompting the scientist to retreat.
Returning to Faust's Hokuto base, Evolt comments to the scientist that that's the first time he's ever been wrong, to which Shinobu admits that he overestimated the two Riders. The two are then informed by Utsumi that Gentoku Himuro and Kazumi Sawatari are sneaking around their base.
As Gentoku and Kazumi made their escape with assistance from Build and Cross-Z Magma, Shinobu showed up as Build NinninComic to fight Build after Utsumi was knocked out of his Mad Rogue transformation and Cross-Z Magma escaped with Gentoku and Kazumi. Declaring to his son that Evolt would destroy the Earth and that there was nothing he could do about it, Shinobu caused Sento's Build Driver to teleport him outside. He then told Utsumi that Build had escaped, neglecting to mention the role he played in it. Meeting with Evolt, the alien entity commented on how Shinobu had let Build get away again, to which Shinobu notes how strong Build is. Shinobu then states that Evolt might have to purify the last three Lost Bottles himself and Evolt replies that they are almost ready to make a new world.
After Evol was destroyed by Build Genius Form, Shinobu swooped in as Build HawkGatling and collected the three Lost Bottles Evolt had dropped before de-transforming and stating that everything had gone exactly according to plan.
True Colors revealed
Shinobu reveals that he was only pretending to be on Evolt's side and places the Evol Driver inside a metal cannister to prevent Evolt from regenerating from the DNA inside it. Taking the Kamen Riders to the Pandora Tower, Shinobu places the three Lost Fullbottles in the Black Pandora Panel and states that he was only working with Evolt so he could complete it, as when it was finished it would allow for warp travel between worlds via wormholes. Shinobu goes on to say that Evolt sought to complete the Black Pandora Panel so he could use it to warp between planets and make interplanetary travel less energy-consuming for him. Sento then criticizes his father for lying to him and his mother and causing the deaths of countless people in order to complete the Black Pandora Panel, but Shinobu tells him that it was all necessary to defeat Evolt.
Nariaki Utsumi then appears and reveals that he is possessed by Evolt, who was aware of Shinobu's intentions of betraying him and sent a fraction of his essence out to possess Utsumi right before he was destroyed. He then fatally wounds Shinobu by injecting him with venom before transforming into Kamen Rider Mad Rogue and engaging the Kamen Riders, save for Sento, who had gone over to tend to his father. Asking Sento if he had gotten taller, Shinobu tells his son of a White Pandora Panel and gave him the blueprints of Cross-ZBuild Form he had created to defeat Evolt before passing away and dissolving into purple mist.
Shinobu Katsuragi was revived in the New World, where he worked with Prime Minister Taizan Himuro and Gentoku Himuro to develop the Build Driver to defend Japan and the world from threats like the Blood Tribe.
- Shinobu shares similarities with King/First OOO from Kamen Rider OOO, as both of them shares same rider system with the protagonist but acts as the catalyst for every bad things happened in their respective series. However, while the King acts as a predecessor villain to Eiji long before the latter, Shinobu transforms into Build after his son gains the mantle. Also unlike the first OOO, Shinobu is more of a false villain rather than a straight up villain.
- Despite being a false antagonist with well intentions, Shinobu's actions in service of Faust has caused deaths of countless innocent people and fatal consequences, something he's being torn and remorseful about.
- Shinobu shares similarities with Sou Fueki from Kamen Rider Wizard. Both of them are responsible for the majority of their series' events (Sky Wall Incident and the Sabbath), and both of them manipulated heroes into their own plans while causing deaths of many people. They also cared about their children deeply. However, while Shinobu shows remorse over every actions he caused that were actually Necessary Evil, Fueki shows no regret over starting Sabbat as long as he could save Koyomi (in spite of feeling guilty for the spawn of Phantoms).