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Ikazuchi (雷［イカヅチ］) is a member of MetsubouJinrai.NET and a supporting antagonist in Kamen Rider Zero-One.
He is originally an Astronaut-Type HumaGear named Uchuyaro Raiden (宇宙野郎雷電 Uchūyarō Raiden, lit. Spaceman Raiden) in charge of Zea and the "older brother" of Uchuyaro Subaru. In reality, he was actually a sleeper agent working for MetsubouJinrai.net and transforms into Kamen Rider Ikazuchi (仮面ライダー雷［イカヅチ］ Kamen Raidā Ikazuchi, lit. "Masked Rider Thunder").
Ikazuchi is portrayed by Daichi Yamaguchi (山口 大地 Yamaguchi Daichi), who previously portrayed Kimura/Kamen Rider Verde in Rider Time: Kamen Rider Ryuki. This makes Daichi the first actor in the Kamen Rider Series to performed the roles of two different Riders from different series and eras within the same year. As Kamen Rider Ikazuchi, his suit actor is Hajime Kanzaki (神前 元 Kanzaki Hajime).
Uchuyaro Raiden was created to maintain the Ark once it had launched. However, the Daybreak Town Accident prevented the launch from occurring. During the course of the Accident, Raiden's programming was compromised by MetsubouJinrai.NET, who installed new protocols that were undetectable by Raiden himself so that he could serve as a sleeper agent. Hiden Intelligence then shut Raiden down due to him no longer having a task to fulfill. When Zea was successfully launched, Raiden was reactivated and assigned to the satellite to maintain it. However, he unknowingly began leaking Zea's data to MetsubouJinrai.net.
After Aruto summoned the Rise Hopper while he and Subaru were in the process of returning it to Zea, Raiden returned to Earth and stormed into Aruto's office. He confronted the young CEO and suggested that he should resign, angered that he carelessly summoned the RiseHopper after returning it back to space. Aruto apologized and exclaimed that he didn't know. Subaru was satisfied with this answer and began to leave, but Raiden stopped him and continued to berate Aruto and Jun Fukuzoe. Raiden then brought Aruto to the Hiden Space Development Center to give him an appreciation for the hard work that he and his brother do.
Raiden, Subaru, Izu, and Aruto were intercepted by Isamu Fuwa and Yua Yaiba, who asked if Zea was able to detect Humagears who are approaching singularity. Raiden responded that it can, and Fuwa accused him of being a spy for MetsubouJinrai.net due to the kanji for his name being present in the organization's name as well. Raiden responded aggressively, and the two almost had a physical confrontation before being separated by Izu and Yaiba. Subaru began to defend his brother, but the group was interrupted by the arrival of Jin, who stated that he had come to take their Progrisekeys and transformed. Aruto, Fuwa, and Yaiba transformed to fight him and the Trilobite Magia that he had created.
Zero-One was able to defeat Jin in Shining Hopper, causing him to attempt to hack Raiden and Subaru using tendrils. Raiden pushed Subaru out of the way to protect him and was pierced by both tendrils. However, he resisted the hacking and removed the tendrils form his body, leading Jin to retreat while commenting that it was no wonder how Raiden survived the Daybreak Town Accident.
Inside the Space Development Center's observatory, Raiden and Subaru related Raiden's history to the group. Raiden stated that he is training Subaru to replace him. Fuwa still suspected Raiden of being a spy, so the Humagear declared his intention to locate MetsubouJinrai.net's base to prove his innocence.
Once Raiden and Subaru discovered that MetsubouJinrai.net was based in Daybreak Town, Raiden brought Aruto and Fuwa there with him to investigate. In a tunnel leading to the lake where the Ark rests, the group is confronted again by Jin, who referred to Raiden as "Ikazuchi". In response, Raiden's MetsuboJinrai programming began to resurface. This lead Fuwa to conclude that he is a spy, though Raiden continued to insist that he wasn't while resisting the programming. Jin explained that Raiden didn't know he was a spy and reveals that MetsubouJinrai had programmed him to transmit Zea's data to them. He also reveals that when he attempted to hack Raiden, he had installed a program that directed him to bring Aruto and Fuwa to their hideout. Jin then attaches a Forceriser to Raiden, forcing him to submit to his dormant programming. Now loyal to MetsubouJinrai.net, Raiden uses the Forceriser and the Dodo Zetumerise Key provided by Jin to transform into Kamen Rider Ikazuchi.
Aruto and Fuwa transformed to fight Ikazuchi, but he quickly defeated them and took the Biting Shark, Flaming Tiger, Freezing Bear, Breaking Mammoth, Shooting Wolf, and Punching Kong Progrisekeys. Jin then gave him the Sting Scorpion and Flying Falcon Progrisekeys, and he inserted all eight into his Progrise Holders. This resulted in the Progrisekeys' Rider Models being extracted from Zea and entering the Ark, reactivating it. The Ark then created the Assault Wolf Progrisekey.
Aruto transformed into Zero-One Shining Hopper to fight Ikazuchi, and was initially successful in overpowering him. However, the fatigue resulting from using Shining Hopper overwhelmed Aruto and Ikazuchi gained the upper hand. Izu then arrived and supplied Zero-One with the Authorise Buster, which he used to fire a powerful blast at Ikazuchi and cause him to drop the stolen Progrisekeys. Jin recovered the Sting Scorpion and Flying Falcon Progrisekeys, while Izu recovered the rest. Horobi then arrived and gave the Assault Wolf Progrisekey to Jin, but Zero-One fired the Authorise Buster again, resulting in Jin dropping the Progrisekey while avoiding the blast and Aruto being forced out of transformation due to the strain. Fuwa then took the Assault Wolf Progrisekey and transformed into Vulcan Assault Wolf. Ikazuchi attacked Vulcan but to no effect. Vulcan then quickly overwhelmed Ikazuchi and was given the Authorise Buster by Aruto. He used it to fire a construct of Punching Kong's Gauntlet at Ikazuchi, who countered with lightning produced by both hands. However, Vulcan's attack prevailed and destroyed Raiden.
As Jin and Yua Yaiba made preparations to extract Naki from Isamu Fuwa's head, Horobi went to go steal the Progrisekey containing Spaceman Raiden's data back from Aruto Hiden. After holding the HumaGear Midori hostage, Horobi forced Aruto to hand over the key. After the two assumed their Rider forms to fight for the key, Jin Burning Falcon swooped in and stole it from Aruto.
With the data from the Progrisekey, Jin and Naki were able to restore Ikazuchi to a new body, reuniting MetsubouJinrai.NET at last.
Naki was later approached by Azu, the Ark's secretary, who collected the data on Naki's Singularity in order to use it to reawaken the Ark.
With all four members of MetsubouJinrai.NET fully reassembled, Ikazuchi and the others joined together to use their combined data to fully bring back the Ark. Upon manifesting in a physical, liquid metal form, the Ark flew into Horobi to possess him, triggering an explosion that damaged one of Naki's earpieces. Ikazuchi later repaired Naki before going out to confront Kamen Rider Zero-One alongside the other members of MetsubouJinrai.NET and Ark-Horobi.
Later on, Ikazuchi and the rest of MetsubouJinrai.NET were met by a massive army of A.I.M.S. soldiers when they arrived to raid their base. After emitting a signal to paralyze the ordinary A.I.M.S. soldiers, Ark-Zero, flanked by Kamen Riders Horobi, Naki and Ikazuchi, faced off against Kamen Rider Thouser and his two Battle Raiders. Ikazuchi and the others fought the Battle Raiders while Ark-Zero dealt with Thouser. Thouser fought off the MetsubouJinrai.NET Riders, but was decisively beaten by Ark-Zero.
Ikazuchi later led the Ark to Hiden Intelligence's space center. As they advanced on the building, Ikazuchi had flashbacks to his time working for Hiden, but when the Ark noticed Ikazuchi told it that it was nothing before the two continued on.
After Ark-Zero and Ikazuchi retreated back to MetsubouJinrai.NET's base, Ikazuchi continued having flashbacks to his memories of his "brother" Subaru. Eventually, remembering his time as an employee of Hiden, Ikazuchi left MetsubouJinrai.NET's base and went to HIDEN Manufacturing to meet with Aruto and help him destroy the Ark. Ikazuchi informed Aruto that the Ark intended to take over Satellite Zea and accompanied Aruto and Jin when they went to confront the Ark at Daybreak Town. When the two arrived at the entrance however, the Ark (in the body of Horobi) appeared accompanied by Naki and took out Jin before revealing that he had anticipated that Ikazuchi's lingering feelings for his brother would lead him to go to Aruto, and that he had counted on that in order to get Ikazuchi to lead Aruto to him. The Ark then transferred its essence from Horobi to Ikazuchi to possess him and transformed him into Kamen Rider Ark-Zero as Aruto became Kamen Rider Zero-One.
The Ark was later driven from Ikazuchi when Ark-Zero was defeated by Kamen Rider Zero-Two. Horobi then showed up to lift the battered Ikazuchi over his shoulder before walking away with him.
Raiden is a HumaGear with an aggressive and passionate personality. He does show immense care for his current model brother Subaru, even willing to risk his life to shield Subaru from Jin's hacking ability. His programming had been compromised by MetsubouJinrai.net during the Daybreak Town Accident, but continued to function normally as a sleeper agent. When MetsubouJinrai.net was ready to enact their plan to construct the Assault Wolf Progrisekey, Jin reactivated his corrupted programming. Despite initially being able to resist, the use of a MetsubouJinrai Forceriser bested him. Thus, he became loyal to MetsubouJinrai.net, though his hotblooded nature remained when fighting as Kamen Rider Ikazuchi.