Gai Amatsu is the former CEO of ZAIA Enterprise Japan and one of the main characters of the first Reiwa era installment in the long-running Kamen Rider franchise, Kamen Rider Zero-One, at first appearing as one of the main antagonists and the rival of Aruto Hiden before joining the heroes in the final arc and becoming an anti-hero. He also appears as the main protagonist of the two-part Blu-Ray mini-series Project Thouser, and one of the two main characters of the web special Kamen Rider Genms -The Presidents alongside Kuroto Dan.
He is Yua Yaiba's superior, the creator of Satellite Ark and the benefactor of A.I.M.S.. He at first appears opposed to Aruto due to his goal of destroying all HumaGears and acquiring Hiden Intelligence, but later relinquishes his buyout of the company and joins Aruto in stopping the Ark.
By inserting both a Progrise and ZetsumeRise Key into the ZAIA ThousanDriver, Gai transforms into Kamen Rider Thouser.
After ZAIA Enterprise Japan went defunct, Gai founded his own company in Thouser-Intellion, which he envisioned as a modern intelligence provider. He also gained his own Humagear secretary in Rin.
He is portrayed by Nachi Sakuragi.
From a young age, Gai was inspired to pursue a career in technology by Hiden Intelligence. As an adult, he joined ZAIA Enterprise and eventually rose to become CEO of their Japanese branch. During this time, Gai finally got the chance to work with his idol Korenosuke Hiden, founder of Hiden Intelligence, when ZAIA and a multitude of other companies collaborated with Hiden to create Daybreak Town, a town autonomously run entirely by HumaGears. Gai worked with Korenosuke to design an AI satellite known as the Ark for the purpose of overseeing communications within the town, but during their time together Gai had a falling out with Korenosuke over the idea of HumaGears, believing that it would be better to enable humanity to evolve by themselves than to replace them with HumaGears. Gai sabotaged the Ark satellite and inadvertently caused the destruction of Daybreak Town, leading to the formation of MetsubouJinrai.NET.
In the present day, Gai would continue to pursue his anti-HumaGear agenda by exploiting the attacks of MetsubouJinrai.NET to frame HumaGears as killing machines, sinking Hiden Intelligence's stock and allowing ZAIA to buy out the company. As CEO of Hiden, Gai deactivated all HumaGears and attempted to remove them from society, but his plan was thwarted in advance by the legacy of Korenosuke Hiden. Korenosuke had made sure to back up all the HumaGears' data in the Progrise Keys, which he kept under his own personal patent rather than that of Hiden Intelligence, enabling them to be passed to his grandson Aruto Hiden.
In wake of the Ark's reemergence, Gai would be forced to team up with his old enemies Aruto and Isamu Fuwa in order to combat it. After being reunited with a new model of his beloved robot dog Thouser, thanks to Hiden Intelligence, Gai would rescind ownership of the company and give it back to Aruto Hiden. Because of his mismanagement in handling the Ark crisis however, Gai was demoted from his spot as CEO of ZAIA Japan by main branch representative Williamson Yotagaki and reassigned to work in the "Thouser Department", where he would become Thouser to battle threats to ZAIA. Following the defeats of the Ark and MetsubouJinrai.NET, Gai would be content to work in his new position, now with a team of Thouser dogs assisting him.
At first glance, Gai appears to be an affable and honest businessmen fully committed to helping humanity evolve. He is a very charismatic speaker skilled at spinning public opinion in favor of himself. He is a master at manipulating the media and seizes upon every opportunity he can to give a good image to ZAIA while sinking the perception of his rivals, namely Hiden Intelligence. Beneath his affable front however, Gai is a very arrogant and cold individual committed only to the expansion of his own capital. He sees HumaGears as a threat to humanity and is willing to take whatever underhanded means he can to stop their insertion into society. At the same time, Gai shows little care for the lives of other humans, and is perfectly willing to sacrifice people's lives in order to achieve his vision of human evolution ushered in by ZAIA. He has no remorse for how his actions led to the Daybreak Town disaster, the destruction of the town having gone exactly as he planned, and even boasts to his assistant Yua that it was he who caused the Ark to run rampant and ultimately destroy the town.
In contrast to his demeanor in public, in private Gai acts very haughty and egotistical. He seems to enjoy flaunting his authority over those who are in no position to resist, torturing Fuwa with the AI chip he implanted in his mind as a way of showing off his hold on him. He treats his assistant Yua little better, and frequently abuses her as well should she do anything to displease him. While he normally stays on the sidelines, Gai is perfectly capable of taking to the battlefield as Kamen Rider Thouser if necessary, and indeed he seems to enjoy the thrill of fighting. He revels in the chance to show off his power as Thouser and, in spite of differing visions, appears to see Aruto as a worthy rival. At the same time, Gai is not above using dirty tactics in combat, jamming Aruto's Driver with the Metalcluster Hopper key to make it so Aruto couldn't transform without being possessed by the Ark.
Despite his cruel demeanor for most of the series, a softer side to Gai is eventually revealed when he reunites with beloved robot dog Thouser. From there, Gai would come to see the error of his ways and side with Aruto as a way of atoning for his past wrongs, giving Hiden Intelligence back to him and cutting ZAIA's influence over AIMS in the process. Despite losing his position as CEO for his mismanagement of the "Ark" crisis, Gai would be content to serve in ZAIA's Thouser Department alongside his dozens of Thouser dogs.
Kamen Rider X
Kamen Rider Amazon
Kamen Rider Super-1
Kamen Rider ZX
Kamen Rider Black/RX
Kamen Rider Kuuga