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|“||My brilliance... and research... are the only things of value. They are the truth of this world!||„|
|~ Ryoma Sengoku while being confronted by Kaito.|
Ryoma Sengoku is a researcher for the Yggdrasill Corporation who created the Sengoku and Genesis Drivers and one of the main antagonists of Kamen Rider Gaim. With his Genesis Driver, Ryoma has the ability to transform into Kamen Rider Duke by inserting the Lemon Energy Lockseed.
Ryoma works under Takatora Kureshima, the head of Yggdrasill's research and development branch. Unbeknownst to Takatora, Ryoma is secretly plotting to overthrow him and use the Helheim Forest situation to claim power for himself.
Ryoma later returns as the secondary antagonist of the Gaim portion of Movie War Full Throttle, having been revived by the Megahex collective to assist it in assimilating Earth and Helheim. Ryoma also appears as a supporting character in Kamen Rider Gaim Gaiden: Kamen Rider Zangetsu, a background antagonist in Kamen Rider Gaim Gaiden: Kamen Rider Baron, and the main protagonist of the V-Cinema film Kamen Rider Gaim Gaiden: Kamen Rider Duke.
He was portrayed by Tsunenori Aoki.
Ryoma was among the children raised in the Yggdrasill Corporation-run Zawame Child Care Facility where he was conditioned to become a scientist for Yggdrasill, eventually becoming a leading member of its Scientific branch.Ryoma would eventually meet and become friends with Takatora Kureshima, head of Yggdrasill's R&D branch. Together, the two created and developed the Sengoku Drivers, which Ryoma named after himself.Ryoma later received a report from his subordinate Yoko Minato of an image appearing to be the Overlord Inves Demushu. He neglected to tell Takatora about its discover due to Takatora's philosophy of putting humanity first.
Beat Riders Saga
Ryoma informed Takatora about the new Driver model, which Takatora offered to test the belt. Ryoma later attempted to get the 7 prototype Sengoku Drivers in the Helheim Forest. Though Takatora did not want any outsiders to be in the forest, Ryoma told Takatora to not destroy his precious work. During the Inves breakout of this event as they run rampant to Zawame City, Ryoma aids Gaim through the use of the Yggdrasill's tower through the use of a cloaking mechanism and beam weaponry.
Ryoma later created the Yomotsuheguri Lockseed in an attempt to harness more power from Helheim. However, after discovered that the Yomotsuheguri Lockseed drained the lifeforce of its user, Ryoma abandoned it. Ryoma also noted that the first Lockseed he created was dubbed the Ringo Lockseed which gives a potent amount of power that allows users to manipulate Cracks at will. However, the Ringo Lockseed overwhelmed its user by spouting Helheim vines from the Ride Wear. Ryoma also worked on a successor prototype of the Suika Lockseed dubbed the "Watermelon Lockseed" because the Suika Lockseeds were hard to come by and had to recharge. This Lockseed was scrapped due to the fact that the output of the Watermelon Lockseed was inferior to the newly created Energy Lockseeds and that the Watermelon Lockseed drains the stamina of the user much more quickly.
Kamen Rider Gaim Gaiden: Kamen Rider DukeYggdrasill fell under attack from Kugai Kudo and the Black Bodhi. Kudo had previously been a researcher for Yggdrasill who was sent into limbo after a test of the Zakuro Lockseed developed by Ryoma went wrong. Sending his brainwashed followers to suicide bomb Yggdrasill in order to test Ryoma, believing that with Ryoma's assistance he can become a god. Ryoma and Takatora later manage to unearth the location of Kudo's artificial Lockseed warehouse and go there to confront him. Transforming into Kamen Rider Duke, Ryoma battles Kudo as Armored Rider Saver, Ryoma manages to defeat him by damaging his Sengoku Driver, rendering him unable to maintain his physical form.
Ryoma had Takatora test the Genesis Driver, noting its impressive strength. Ryoma later watched Sigurd kill Ryoji Hase. Ryoma then introduced himself to Kouta and Kaito and asked for their permission to continue using them to complete his quest for power, but the two escape. Ryoma later discovered that the Genesis Core slot and the Lemon Energy Lockseed is stolen and pondered why someone would take an incomplete core slot prototype.
Ryoma used the data received from Kouta's Sengoku Driver to improve the mass-production models. He also examined the data from Jimber Lemon Gaim and Marika's fight and decided to test how his Genesis Driver would do on Kouta. Transforming in Kamen Rider Duke, Ryoma easily defeated both Jimber Lemon Gaim and Baron.
Ryoma later attempts to trick Kaito into finding the Over Lords without the equipment to combat them. Ryoma also apologized to Kaito for what Yggdrasill did to his family, by buying and destroying the construction factory Kaito's father owned.
Later, when a Crack appears on a bridge in Zawame City, Takatora sent Ryoma down to the other side of the Crack in the Helheim Forest. Ryoma later explains Kouta what Project Ark and Yggdrasill plans to reduce humanity 1 billion in order to eliminate the potential 6 billion Inves, as well as how the Sengoku Driver will help the remainder of humanity as it converts Helheim's fruits into Lockseeds and enables the wearer to absorb the nutrients safely without side effects. As the Crack closes, Kouta steals Yoko's Peach Energy Lockseed and rushes to HQ to destroy the Scalar System.
Kamen Rider Gaim Gaiden: Kamen Rider Zangetsu
Yggdrasill falls under attack from a mysterious Armored Rider capable of controlling the power of Helheim. From the Rider's power to create Cracks, Ryoma is able to identify the Lockseed it is using as the Ringo Lockseed, though he does not inform Takatora of this. As Takatora investigates the unknown Rider's origins, Ryoma gives him the Watermelon Lockseed to Takatora for him to use with his Sengoku Driver as a back up in case he loses his Genesis Driver.
The Armored Rider attacking Yggdrasill is later revealed to be Takatora's childhood friend Touka Akatsuki, who was raised and experimented on in Yggdrasill's Zawame Child Care facility. After Takatora defeats her and spares her life, Ryoma approaches Touka and reveals himself as another orphan raised in the facility before killing her to take the Ringo Lockseed back without Takatora knowing.
Kamen Rider Gaim Gaiden: Kamen Rider Baron
Ryoma Sengoku met with Alfred to discuss the purchase of Yggdrasill's Sengoku Drivers. However, Ryoma supplies him with a Genesis Driver and the prototype of the Dragon Fruits Energy Lockseed instead, plotting to use Alfred as a guinea pig to test the Lockseed out. After the Lockseed transformed Alfred into a pseudo Over Lord, Ryoma sent Yoko to give Kaito Kumon the Ringo Lockseed to test its strength. Baron Ringo Arms manages to destroy Alfred, but the Ringo Lockseed is also destroyed in the fight.
Helheim & Over Lord Saga
Ryoma later apologized to Mitsuzane for giving Kouta classified information. He realizes that Kouta is being supported by someone else when Kouta uses the Kachidoki Lockseed and tells Mitchy to find out who it is. Mitsuzane later informs him and along with the other Yggdrasill employees of creatures even more dangerous to humanity than the Inves. Realizing that their chance for power is dwindling, Ryoma provides Sid with another Cherry Energy Lockseed, so as to give Sid a chance to kill Kouta.
DJ Sagara later and Ryoma tells him about how the history of Helheim and how it has affected human civilization, before disappearing after instructing them to find the Overlords.
Seeing that the Sengoku Driver isn't a match against an Overlord, Ryoma let's go of Kaito from his group. However, Yoko gives Kaito a Genesis Driver replacement to provide him with another chance. When figuring out how to find the Over Lords, Mitsuzane tells them that they can easily find the Over Lords if they adhere to his plans.
After Takatora discovered the Over Lords, Ryoma attempts to dispose of Takatora and transforms into New Generation Rider Duke. Ryoma defeats Takatora, with Sid throwing him off a cliff. They later go to Yggdrasill's headquarters and erase all of Takatora's records.
However, Sid destroys all of the equipment around the tree, causing the Headquarter's Crack to disappear and close. Ryoma then tells Kouta, Kaito, and Mitsuzane to stop Sid from getting the Forbidden Fruit. When Demushu attacks Zawame City, Duke cuts off all communication in the city save the forces fighting Demushu. When Helheim's plants begin to absorb Yggdrasill Tower, Duke abandons Marika and the other Yggdrasill employees and escapes in a rocket, causing him to lose Marika's loyalty.
Forbidden Fruit Saga
Ryoma later attends a holographic conference between the executives of Yggdrasill's international branches. The executives threaten to arrest him due to the Japanese branch's responsibility disaster, but Ryoma uses a bug in the executives' phones to expose Project Ark and Yggdrasill's plans to cull the population to the world, sparking a global panic.
Ryoma then goes back to Zawame. He meets Kouta in Team Gaim's garage and mocks him about Takatora fate, provoking a fight between the two. However Armored Riders Knuckle and Baron appear and ambush him. Ryoma surrenders and reveals to the alliance of a secret entrance to Yggdrasill Tower before leaving them.
While Oren and Hideyasu fight the Inves, Ryoma and Kouta enter Yggdrasill Tower. However, they are confronted by Shinmugurun. Kouta fights the Overlord, but isn't able to defeat it. Duke steps in and takes down Shinmugurun easily. However, he doesn't kill him to see to collect data on the Gaim Kiwami Arms. After the battle is over, he makes a thought that it will be interesting to collect more data about Kouta's new power.
Arriving on the site where the kidnapped citizens are, Ryoma leaves Gaim to fight Redyue. Ryoma then reboots the Master Intelligence System to access records prior the Inves invasion. Upon discovering Rosyuo's name while analyzing the footage, he theorizes that the White Over Lord is the one holding the Forbidden Fruit.
Ryoma later secretly follows Kouta and Kaito to gather data of Rosyuo's power in Helheim. Despite the Forbidden Fruit from Rosyuo expiring, Ryoma discovers that Rosyuo planted a second Forbidden Fruit in Mai. Ryoma returns to Zawame and forms an alliance with Mitsuzane to extract the fruit. They bring Mai to a hospital where Ryoma examines her body. Sagara then appears, explains his purpose to them before disappearing again. Ryoma informs Mitchy that he can remove the fruit from Mai, but states that Kouta would interfere and gives Mitchy the Yomotsuheguri Lockseed to defeat Kouta with. Ryoma also warns Mitsuzane the consequences of using it before he leaves.
Later, Mitsuzane returns and Ryoma states that he did not expect Mitsuzane to survive. Ryoma reveals to Mitchy that the Forbidden Fruit had fused with Mai's heart and, in order dissect it, Ryoma had to kill her. Enraged, Mitsuzane tries to attack him, but Ryoma disables his Genesis Driver. However, the Fruit turns into an apparition of Mai and disappears.
Ryoma attempts to locate where to fruit is, but he is confronted by Kaito and Yoko, who sought to avenge Mai. Ryoma disables their Genesis Drivers, forcing Kaito to use his Sengoku Driver instead. Because the Sengoku Driver is weaker than the Genesis Driver, Duke defeats him.
However, Kaito consumes a Helheim Fruit, changing him into an Over Lord Inves called Lord Baron. Ryoma attempts to fight Lord Baron but Lord baron easily defeats him. Before Lord Baron can kill him, Ryoma tells Kaito that he won't survive long and falls off the edge the off the building they're on, causing him to plummet to his death.
Movie War Full Throttle
|“||It's been a long time, my friend.||„|
|~ Mecha Ryoma's greeting to the Kureshima brothers.|
Ryoma returns in the film Movie War Full Throttle when he's revived by the mechanical life-form Megahex as Mecha Ryoma Sengoku. Declaring that by becoming one with Megahex he has become equal to a god, Mecha Ryoma equips the Dragon Fruits Energy Lockseed to transform into Kamen Rider Duke and attacks the two Kureshima brothers, swiftly beating them down and forcing them to retreat.
Later the brothers face off against Ryoma again when they return to save Mai from Megahex. While Mitsuzane goes to rescue Mai, Mecha Ryoma fights Takatora in a decisive battle. Takatora uses his Musou Saber to stab through Ryoma's Genetic Ride Wear and kill him. Mecha Ryoma said his last words to Takatora before dying. His Genesis Driver was promptly taken by Takatora to allow him to transform into Kamen Rider Zangetsu Shin again.
- He was named after the Japanese historical figure Sakamoto Ryōma, with his surname being derived from the Japanese "Sengoku" period.
- Ryoma's popularity led to him getting to star in his own V-Cinema movie Kamen Rider Gaim Gaiden: Kamen Rider Duke.
- Despite the complex morality of the show, Gaim's head writer Gen Urobutchi has stated that Ryoma is "the most evil person in Gaim."