Reiko Momoi is the editor of the Atashi Journal. When Natsumi finds her upon arriving in the World of Ryuki, Reiko mysteriously dies, leaving Natsumi as the sole suspect of her murder. However, Ryuki uses the Time Vent Card to alter time and save her, while simultaneously revealing the true murderer.
|Shinji Tatsumi / Kamen Rider Ryuki
Shinji Tatsumiis a young cameraman who works for the Atashi Journal in the Ryuki World, a popular magazine that covers the Kamen Riders and the trials. When the editor of the journal is murdered, Shinji becomes a Kamen Rider to decide the fate of the suspect. Like his namesake in Ryuki, Shinji has the ability to transform into Kamen Rider Ryuki and use the power of his Contract Monster Dragredder. He later appears in Kamen Rider ? Kamen Rider Double & Decade: Movie War 2010 alongside the other Riders of the Nine Worlds to help in reviving Tsukasa and helps him battle Super Shocker, assuming Ryuki Survive with the help from Decade Complete Form's K-Touch.
|Ren Haguro / Kamen Rider Knight
Ren Haguro is a former journalist of the Atashi Journal and Shinji's former best friend, mysteriously leaving the group three years ago without explanation. Ren has the ability to transform into Kamen Rider Knight and use the power of his Contract Monster Darkwing. When Reiko is murdered, Ren enters the Trial to find the Rider who possesses the Time Vent Card. After defeating Scissors, Ren encounters Decade in a brief confrontation before Zolda intervenes. Later while forced to fight Shinji who accuses him of playing a part in Reiko's death, Decade's fight with Imperer stops theirs. Soon after, Decade battles Knight with the former being the superior fighter until Abyss intervenes. After defeating Odin, Ren acquires the Time Vent card at the cost of being too injured to use it himself.
|Kamata / Kamen Rider Abyss
Kamata Kamata is a mysterious man who is the sub-chief editor of the Atashi Journal. In the World of Ryuki, he has the ability to transform into Kamen Rider Abyss with his Contract Monsters Abysslasher and Abysshammer. Once exposed as the one behind Reiko's murder and as an Undead, Narutaki returns Kamata to his homeworld: the World of Blade. As Kamen Rider Abyss, Kamata uses his Final Vent to combine his Contract Monsters into a creature known as Abyssodon a single giant mechanical shark with a chainsaw attachment (giving it the appearance of a sawshark when in use) and machine gun eyes (giving it the appearance of a hammerhead shark when in use).
|Kamen Rider Scissors
Scissors is a cheating Rider who uses the power of his Contract Monster Volcancer. He is labeled by the Journal to have a victory rate of 6.8%. He is removed from the trial by Knight. Appears in Episode 6.
|Kamen Rider Zolda
A public prosecutor who sees Natsumi guilty. Zolda is a Rider who uses the power of his Contract Monster Magnugiga. Appears in Episode 6.
|Kamen Rider Verde
Verde is a Rider who uses the power of his Contract Monster Biogreeza. He lowers his guard when falling for Scissors' trap and is removed from the trial by Volcancer who destroys Verde's Advent Deck. Appears in Episode 6.
|Kamen Rider Tiger
Tiger is a Rider who uses the power of his Contract Monster Destwilder. He is removed from the trial by Zolda's Giga Launcher. Appears in Episode 6.
|Kamen Rider Imperer
Imperer is a Rider who uses the power of his Contract Monsters Gigazelle, Megazelle, Omegazelle, Negazelle, & Magazelle. He is removed from the trial by Decade's Final Attack Ride. Appears in Episode 6.
|Kamen Rider Odin
Odin is a Rider who uses the power of his Contract Monster Goldphoenix. He lets himself be removed from the trial by Knight's Final Vent allowing Knight to take the Time Vent Card. Appears in Episode 7.
|Kamen Rider Raia
Briefly appears in the World of Ryuki. He is also later summoned by Kamen Rider Diend in the World of Shinkenger.
|Kamen Rider Gai
Briefly appears in the World of Ryuki.
The Mirror Monsters are a race of monsters that reside in the Mirror World. They often come into contact with the Kamen Riders of this reality.
In Episode 6, a red Fenghuang monster in a Phoenix-shaped helmet. It is shown briefly fighting Kamen Rider Ryuki alongside Omegazelle and Zebraskull Bronze.
In Episode 6, a blue and yellow gazelle monster that often appears when Kamen Rider Imperer summons it.