This movie is an alternate ending to the series, taking place after the events of episode 46. With only six Riders remaining in the Rider War, Shirō Kanzaki feels that time is running short.
As Yui's life grows short, she shows Shinji Kido and Ren Akiyama pictures of her childhood drawings, explains the reasoning for the Mirror Monsters and Shiro's reason to start the Rider War.
Shinji bumps into Miho Kirishima after she cons another wealthy man and takes Shinji's wallet. He chases after her, the two reveal themselves as Riders to each other, before they're forced into fighting Mirror Monsters. Shinji as Kamen Rider Ryuki tries to convince Miho as Kamen Rider Femme not to fight and she rejects.
The other Riders fight with one another, with their own goals present. Miho fights to seek revenge on Takeshi Asakura who murdered her sister and to resurrect her. Ryuga fights so he can be a real human in the real world.
Takeshi as Ouja battles Miho as Femme and after a few blows are exchanged, Femme is on the losing side. Ouja unites his monsters to form Genocider and aims to finish Femme. He's interrupted by Ryuga, who attacks him with his own Final Vent, destroying Genocider and reverting Ouja to his blank form. Femme finds Ouja and hits his Advent deck, shattering it, which leaves him unable to survive in the Mirror World. He disappears after attempting to kill Femme before disintegrating, making him the first of the six remaining Riders to be finished.
During the battle, Shuichi Kitaoka, as Kamen Rider Zolda trades blows with Femme, injuring his wrist and leaving him unconscious. He tells Goro Yura he'll fight again, but he changes his mind and forfeits his mission as a Rider, instead choosing to date Reiko Momoi.
During the battle, Miho mistakes Shinji as Ryuga. She treats him to dinner, claiming Shinji saved her life and assisted her in getting a step closer to winning the Rider war with Shinji unsure of her sudden kind attitude to her. While in the bathroom, the mirror Shinji enters, and disguised as the real one, tries to throw Miho off the roof of a building. As she realizes that he is not Shinji, he reveals himself as Ryuga, and Miho transforms to Femme to fight him. Ren as Kamen Rider Knight and fighting another Mirror Monster, notices Ryuga and Femme fighting, mistaking Ryuga to be Shinji. Femme is mortally wounded, but saved by Shinji as Ryuki who then catches a glimpse of his own mirror doppelganger before Ryuga leaves. After leaving the Mirror World, Shinji and Miho share a final moment together, before Miho dies from her wounds.
Ren returns to Shinji, thinking Shinji has finally realised the meaning of the Rider War and demands the two of them fight, while Shinji rejects Ren bluntly and claims he never thought of that.
Shinji remembers that he had previously known Yui as a child, and had abandoned her. This made her create a doppelganger Shinji in the Mirror World, then revealed as the mysterious Kamen Rider Ryuga, a darker form of Ryuki. Shinji feels that it was his fault that resulted in the creation of a darker version of himself. Taking Shinji's guilt into account, Ryuga tricks Shinji into uniting both bodies so he can be a real human, taking over Shinji's body in the process.
This is seen by Ren, who transforms into Knight and battles Ryuga, the two of them fighting while Yui's life shortens further. After defeating Knight, Ryuga tries to strike the killing blow before Shinji within Ryuga struggles. The two beings separate and they fight each other. After a climatic battle, Ryuga is killed by his original counterpart via Ryuki's Final Vent.
Ren tells Shinji that he must win, and that Shinji agrees he will not let up and will fight Ren willingly. Before they fight, Shinji and Ren transform into their respective Survive Rider forms and face a horde of Hydragoon Mirror Monsters as the movie ends.Takamasa Suga as Shinji Kido, Mirror Image Shinji KidoSatoshi Matsuda as Ren AkiyamaAyano Sugiyama as Yui KanzakiKenzaburo Kikuchi as Shiro KanzakiRyohei as Shuichi KitaokaTomohisa Yuge as Goro YuraTakashi Hagino as Takeshi AsakuraKanji Tsuda as Daisuke OkuboSayaka Kuon as Reiko MomoiHitomi Kurihara as Nanako ShimadaKazue Tsunogae as Sanako KanzakiNatsuki Katō as Miho KirishimaEugene Nomura as Restaurant Customer (DC ver. only)Yoji Sawamukai (Played as "沢向 要士") as Kazuo MizuokaErena as Miho Kirishima's Older SisterYoshikazu Ebisu as Owner of MansionBengaru as Taxi DriverToshiki Kashu as Restaurant Staff (cameo)Rina Akiyama as Amusement Park Staff (cameo)Yūsuke Tomoi as Takeshi Asakura's Victim (cameo)Jun Kaname (cameo), Tōko Fujita (cameo), Jun Yamasaki (cameo) as Okonomiyaki Restaurant CustomersAkiyoshi Shibata (cameo) as Okonomiyaki Restaurant StaffHiroyuki Shibamoto, Shigenori Sōya, Yoshimasa Chida, Katsumi Shiono as Sheerghost/Raydragoon voiceTsuyoshi Koyama as Visor VoiceTheme song"Alive A life -Advent Mix-"Lyrics: Yuko EbineComposition: Kohei WadaArrangement: Takahiro AndoArtist: Rica Matsumoto