Accepting his role as the harbinger of destruction, Tsukasa Kadoya embarks on a relentless quest to battle and capture various Riders from across the multiverse, harnessing their essence into cards. He is accompanied by Yuriko Misaki, who tries to aid him, but their path soon crosses with Natsumi Hikari and Yusuke Onodera, who seek to halt Kadoya’s rampage through their own methods. In a poignant moment, Natsumi attempts to jog Kadoya's memory of his former self, but her efforts are futile as he dismisses her and proceeds to confront Onodera alongside Misaki. Natsumi is left despondent until the reassuring voice of Kiva-la reminds her that Kadoya holds the key to thwarting him, while Onodera could provide her with the necessary capabilities to do so.
In parallel, Natsumi’s grandfather, Enjiro Hikari, engages with his friend Ryu, who provides him with the Doctor Death Gaia Memory, effectively turning him into Super Doctor Death. Together with the enigmatic Narutaki and Bee Woman, they form a faction known as Super Shocker, seizing the opportunity created by Kadoya’s actions through the Neo Organism.
As tensions rise, Daiki Kaito confronts Kadoya with a harsh revelation — Misaki had been killed by Bee Woman, a truth that Kadoya's denials fail to erase. After Kadoya decimates Onodera and the remaining Riders from the multiverse, Natsumi undergoes a transformation into Kamen Rider Kiva-la with the support of Kiva-la to confront Kadoya. In a dramatic twist, Kadoya grants her the moment to end his life, passing on his cards and urging her to hold onto their memories before his passing. Following this, Kaito and Natsumi find themselves teleported to Wataru Kurenai, who clarifies that Kadoya's tragic journey ultimately revitalized the multiverse, enabling the continuation of their stories by crafting new memories.
Upon returning to their own reality, Natsumi and Kaito exert their efforts to revive Kadoya using his camera. However, they soon face an onslaught from Super Shocker. With the dynamics shifting, Kaito, Misaki, and a resurrected Onodera courageously fend off the attackers while Natsumi scours for Kadoya’s camera. In a heart-wrenching twist, Misaki sacrifices herself to injure Bee Woman, who then retreats to Super Shocker’s fortress, where she releases the Neo Organism, which subsequently absorbs her and morphs into Doras.
Natsumi struggles to develop Kadoya’s photographs, but despite her efforts, his face eerily does not manifest in any of them. Passing the camera to Kaito and Onodera, they collectively refuse to let his memory slip away. With the combined memories of the Riders from the Nine Worlds, they succeed in reviving him. During the climactic battle against Zol and Doras, as the Super Crisis Fortress unleashes its devastating power, Kadoya, Kaito, Natsumi, Onodera, and the Nine Worlds Riders unite to confront their formidable foes. The Neo Organism falters, reverting to its original form and orchestrating an assault with a mammoth robot.
In a series of flashbacks, we glimpse the diligently woven past of Sokichi Narumi and his apprentice Shotaro Hidari, who infiltrate a clandestine facility in search of the "Child of Fate." Their mission becomes fraught with peril as Sokichi engages in combat against guards while Hidari attempts to follow a cryptic young man with the potential to create Gaia Memories, but inadvertently leads to the young man’s capture. However, Sokichi manages to rescue the boy, bestowing upon him the name Philip, inspired by his literary idol, Philip Marlowe. Tragically, Sokichi meets his end at the hands of the guards, leaving a dying plea for Hidari to fulfill their unfinished business before they both transform into Kamen Rider W to obliterate the guards and evade the crumbling installation.
Fast forward to present day, Hidari reminisces about his cherished Christmas with Sokichi until Akiko Narumi, Sokichi's daughter, brings him back to reality, requesting assistance with decorating their office. Their routine is interrupted by a pop star, Asami Mutsuki, who seeks their help, claiming to be haunted by the ghost of her sister and former partner, Erika. Despite reluctance from the Fuuto Irregulars, Hidari and Philip accept the case. Their investigation leads them to Erika's grave, where they converse with the cemetery's enigmatic keeper, Father Roberto Shijima, whom Hidari finds suspicious due to his peculiar perspectives on resurrection.
As the investigation unfolds, Akiko discovers that Asami halted the case, swayed by Shijima's dark promise to facilitate her reunion with Erika. Realizing Shijima's deceit, he attempts to entrap the women. However, Hidari and Philip act swiftly to intervene, only to face Sokichi’s spirit as Shijima transforms into Death Dopant. Engaging in fierce combat, Hidari faces an internal struggle while Philip tries to remind him that Sokichi has passed, yet they are momentarily overpowered.
In the aftermath of the encounter, a shaken Hidari contemplates quitting, but Akiko's encouragement steadies his resolve. Renewed, they revisit the installation, recalling the genesis of their journey together. They ascertain Shijima's true identity as the culprit. When Akiko follows Asami to confront Shijima, he resorts to his desperate measures, summoning Sokichi's spirit. This leads to a confrontation where Hidari and Philip battle against Shijima who reverting into Dummy Dopant. A surprising interruption from the Sonozaki family allows Shijima to slip away, prompting a chase by Hidari and Philip.
Simultaneously, a fortuitous encounter leads Kadoya, Hidari, and Philip to cross paths again while pursuing Shijima. United by their shared purpose, they coordinate with Kaito, Natsumi, Onodera, and the Nine Worlds Riders to bring down the Super Crisis Fortress. The climax intensifies as the fortress begins to implode, resulting in the Doctor Death Memory detaching and restoring Enjiro. As the ancient threat of the Neo Organism continues to grow, Kadoya, Hidari, and Philip consolidate forces to dismantle it once and for all.
As the Riders take their leave to return to their respective realities, Kadoya utilizes his dimensional powers to draw forth an alternate reality version of Sokichi, providing much-needed closure to Hidari. In the end, Kadoya embarks on a continued journey through the multiverse accompanied by Kaito, Onodera, and the Hikari family, while Hidari and Philip engage in their celebration, beneath the ominous proclamation of a man robed in red declaring that W is no longer the sole Kamen Rider in Fuuto.
