The spoilers for Kamen Rider Fourze's portion in Kamen Rider x Kamen Rider Wizard & Fourze: Movie Wars Ultimatum has just surfaced online courtesy of one reliable spoiler provider!
Spoiler alert! Read at your own risk!
Ryusei and Inga are investigating a crime organization in South America. They hear from the boss of the organization that there's a Switcher in Japan, so they both head back. Back at New Amanogawa, Gentaro is trying his best to be a good teacher, suddenly Jiro announces that he's the leader of the Monster Alliance.
He reveals his mission to destroy Yuki's space capsule, and runs out of the classroom. Gentaro chases after him, when he's caught up Jiro transforms into Sannagiman. Gentaro transforms, they fight and Gentaro is winning. Banba appears, blocks Fourze's attack and transforms into Hercules Zodiarts.
The movie doesn't really explain where Banba got his Switch from. But Akumaizer paid him to work for them. He just comes off as greedy person. Ryusei eventually arrives in Japan and reunites with Gentaro, as the Switcher he was chasing is Banba.
In order to celebrate Yuki's successful mission, Gentaro gathers all the Kamen Rider Club members to surprise her. Except for Tomoko, who's doing a fan signing event. The camera is showing a fan with a book waiting for her autograph. As she looks up, Ryusei is standing there. They passionately hug in front of the huge crowd that came to the event.
Source: DecaEnd of HJU