The police developed the G3 system to deal with unidentified life forms. The G3 system was designed based on the power of unidentified life form No. 4, Kamen Rider Kuuga. The operator was a police officer named Makoto Hikawa, who was honest but a little rough. Another police department discovered an ancient civilization on a deserted island and decoded it. When the unidentified life forms appeared again and even G3 was no match for them, the mysterious golden Kamen Rider Agito appeared. This Kamen Rider was a young man with amnesia, Shoichi Tsugami, who was initially unable to control himself and attacked G3. Shoichi temporarily lived in Yoshihiko Misugi's house and met Manao Fuuya, who had superpowers. Manao helped Shoichi go out to find his lost memories and met Ryowa Wasahara. Ryo found a notebook among his father's belongings, but the name mentioned in it was unknown. After investigating the cause of his father's death, he found out that he was another Kamen Rider - Glass Brand. Glass Brand is an incomplete Agito, so when Ryo transforms into Glass Brand, posthumous evidence will appear. Once he was in danger, but fortunately he was saved by a young man born with the genetic factor of a super ancient civilization. The unidentified life forms that appeared later were also defeated by Shoichi, Ryo and Makoto one after another. Later, Ryo mistakenly thought that his girlfriend was killed by Agito, which led to a confrontation between Glass Brand and Agito. Because Agito saved G3 many times, G3 joined the battle to fight Glass Brand. Unfortunately, G3 and Agito were unable to defeat the Blademaster. The police saw a more powerful weapon, the G3-X. With the cooperation of G3-X and Agito, the unidentified life form became more and more powerful, but was defeated. The third Kamen Rider was transformed by Kino Kaoru. Although he would prioritize the unidentified life form, he would also deal with the Blademaster and Agito because he thought that he was enough in the world. Later, he was defeated by the enhanced Blademaster, and was saved by Ryo and changed. It turns out that the mysterious young man is the Creator who used the power of darkness in ancient times. This time, he sent the water spirits to fight against the three Kamen Riders and G3. At first, the four were defeated, but Shoichi broke through his fear and made Agito's power rise to a higher level. Then, the four of them joined forces and defeated him. After investigation by the police and Manayo, they found that Shoichi's sister Kisetsuna had also become Agito, and other people with superpowers would eventually become Agito. Manayo also found that her father's death was related to Agito and alienated Shoichi. At this time, the Creator of Darkness personally attacked to take back the power of Shoichi and others. He also decided to kill all humans to prevent more Agitos from being born. He sent the wind, earth, and water spirits, and the final battle between Shoichi, Ryo and Makoto began here.