Kamen Rider × Kamen Rider OOO & W Featuring Skull: Movie War Core

While fighting the male Pteranodon Yummy, Kamen Rider W receives help from Ryu Terui, who is forced to fight without his Rider equipment due to his bride-to-be Akiko Narumi, who wants them to focus on her wedding. After the Yummy escapes, Akiko threatens to call off the wedding, upset that her deceased father, Sokichi Narumi, is unable to attend. Demanding to know why he became a Kamen Rider, the Pteranodon Yummy returns and uses the Memory Gaia Memory on her.

Akiko witnesses a memory from Sokichi's past, where he worked on a case involving opera singer Melissa and an inhuman stalker. While watching Melissa's latest performance, Sokichi met her manager Kozo Yaguchi before Melissa's stalker, the Spider Dopant, attacked. Sokichi fought the criminal before it disappeared with a Gaia Memory dealer named Eren Komori. Despite his partner Seiichiro "Matsu" Matsui's objections, Sokichi continued to investigate Melissa. He later met with his benefactor, Shroud, who told him the Museum is moving forward with their master plan. While meeting with Matsu, Sokichi learned that Yaguchi's previous female clients have gone missing.

Sokichi broke into the Yaguchi Talent Agency, where he found the missing women were being used as test subjects for Gaia Memory research and was confronted by Komori, who transforms into the Bat Dopant. She and the Spider Dopant overwhelm Sokichi, but Shroud gave him the means to transform into Kamen Rider Skull. After receiving a call from a young Akiko and promising to attend her future wedding, Sokichi pursued Komori and the Spider Dopant. He found Yaguchi, who reveals he was only the Museum's Gaia Memory supplier before he was killed by a Spider Bomb concealed in his wife.

The next day, Sokichi deduced that Matsu is the Spider Dopant and confronted him. Exposed, Matsu tried to defend himself until Melissa revealed that Matsu took the Spider Gaia Memory to protect her from Yaguchi and that it warped his mind. Matsu had also previously implanted her with a Spider Bomb that will explode if she touches the person she loves. When he failed to activate it, Matsu went mad and kidnapped Melissa. After killing Komori for impeding him, Sokichi pursued and killed Matsu. As Akiko emerges from the memory, the Pteranodon Yummy escapes.

The Kougami Foundation finds Oda Nobunaga's mummified remains and use it to create a Cell Medal-based homunculus, which escapes and transforms into a monster. It attacks a man, but Eiji Hino transforms into Kamen Rider OOO to fight it off. While pursuing the monster, he finds an injured man and takes him to the Cous Coussier restaurant, where the man introduces himself as Nobunaga, but fails to remember anything else. Hino takes Nobunaga under his wing and helps him get a job at a software company.

The next day, Nobunaga meets a ballerina named Yoshino Akechi and falls in love with her. When the male Pteranodon Yummy attacks them, Nobunaga receives the Birth Driver from the Kougami Foundation's head, Kousei Kougami, and transforms into Kamen Rider Birth to fight the monster. However, Nobunaga then transforms into the monster Hino fought previously and causes Akechi to sprain her leg while attempting to kill her.

As Hino fights Nobunaga, a Greeed named Giru uses Akechi to create a female Pteranodon Yummy, who attacks Hino and Nobunaga. The former destroys it while the latter suffers from Cell Medal breakdown. Visiting a hospitalized Akechi, Nobunaga uses the last of his power to heal her before the scientist Kiyoto Maki gives him three black Core Medals, which enhances Nobunaga's monstrous form. Upon confronting Nobunaga once more, Hino kills him to end his suffering. The black Core Medals fly off, with Hino in pursuit.

Having obtained the most intense memories of Kamen Rider battles, the male Pteranodon Yummy is caught off-guard when the black Core Medals appear, combine with the Memory, and form the giant Kamen Rider Core. It attacks Akiko, but she is saved by Hino, who assures her Sokichi had his reasons for being a Kamen Rider before joining forces with W to fight Core. After taking the fight underground, W and Hino find a crystal that is powering Core and destroy both of them, shattering the components that created it and blasting Hino to Rio de Janeiro. Meanwhile, Terui persuades Akiko to give him his equipment back so he can protect her from the male Pteranodon Yummy, who he destroys with Shintaro Goto's help. With her faith in Kamen Riders restored, everyone hurries back to Akiko's wedding, where Melissa arrives to take Sokichi's place and reveals he was also implanted with a Spider Bomb, which did not die with the Dopant.