Upon arriving in the World of Ryuki, Natsumi goes to the Atashi Journal headquarters to learn about the world's Kamen Riders from its editor, Reiko Momoi. After Natsumi's arrival at the journal's offices, Reiko is mysteriously murdered, leaving Natsumi as the culprit as she had a small fork in her hand. Natsumi is arrested under suspicion of murder, and is to be sentenced with a Kamen Rider Trial: a system where Kamen Riders fight in the Mirror World to determine the outcome of criminal cases. Natsumi calls upon Tsukasa to be her lawyer, who meets with Shinji Tatsumi to hear what he knows of what happened to Reiko. As Shinji reveals that he is Kamen Rider Ryuki and he believes Natsumi was framed, his former friend Kamen Rider Knight is fighting in the Kamen Rider Trial, defeating several opponents. Shinji suggests to Tsukasa that he should fight as Decade in the Kamen Rider Trial to clear Natsumi's name. At the scene, he finds that Ren Haguro was also at the scene of the crime before he is brought into the Mirror World along with the sub-editor of the Atashi Journal: Kamata. Decade and Abyss' fight, however, is interrupted by Kamen Rider Imperer, and Abyss leaves to watch Decade's abilities. Elsewhere, Shinji confronts Ren, believing he is Reiko's real murderer, and he challenges him as Kamen Rider Ryuki. Their fight is also interrupted by Decade, having just defeated Imperer and now turning his sights on Knight, easily overwhelming him in Kiva's various forms with Shinji watching.[6]
龍騎の世界。この世界のライダーを調べるために、「Atashiジャーナル」を訪ねた夏海だが、編集長・玲子(高橋佐衣)を殺害の容疑で逮捕されてしまう。夏海はミラーワールドで仮面ライダーたちが戦い、最後に残った一人が判決を決める仮面ライダー裁判制度で裁かれることになった。
