In 2002, there were many strange cases of missing persons in Japan. In order to investigate the case, reporter Shinji Shirodo went to the home of one of the victims, Koichi Sakakibara, to investigate. During the investigation, he found a card box. Later, Shinji accidentally used the power of the card box to transform into Kamen Rider Ryuki, and met another Rider Akiyama Ren (Kamen Rider KNIGHT) and Kanzaki Shiro's sister Kanzaki Yui. Shinji's purpose as a Rider is to protect humans and stop the fight between Riders. On the contrary, Ren, who doesn't like fighting, is forced to fight with other Riders to save her lover. With the appearance of others, the fight between Riders gradually became fierce. Even though Shinji tried his best to stop it, the victims of the fight continued to appear. Just as the fight between Riders developed to the later stage, Shinji suddenly discovered the reason why Kanzaki Shiro initiated the fight between Riders to save Yui. It turned out that Yui had died when she was a child, and now Yui's life is given by Yui in the mirror world, and this life will be exhausted at the age of 20, and Yui will also disappear. Kanzaki Shirou, who had known about this for a long time, wanted to give the last Rider's life to Unii, so he started a battle between Riders. Shinji knew that the only way to save Unii was to fight, so he had to choose between stopping the battle and saving Unii. On the other hand, Unii, who knew her brother's purpose, was willing to give up her new life in order to stop the battle, and disappeared in front of Kanzaki Shirou. Influenced by Unii, Shinji decided to continue fighting to protect humanity, but unfortunately he was attacked by a monster and died while protecting a girl. Ren became the last Rider and successfully revived his lover, but he was seriously injured and died. After the battle, Kanzaki Shirou returned to the past and started a battle between Riders again, but was stopped by Unii. In the end, Kanzaki Shirou returned to the past, so that the battle between Riders no longer happened, everyone lived an ordinary life, and Unii had died when she was a child.