The movie starts off with 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 Saburo 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 Saburo 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. He’s the one who gives Saburo the Zebar, a device that will enhance his ESP powers. Later it’s revealed that the Zebar is only collecting energy for the Akumaizer.
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.
Banba gathers students by saying he’ll give them ESP abilities, but in reality he places small mind controlling devices on them. Gentaro and his friends arrive, Inga shows a video clip to the students revealing Banba’s real intent and that no one will actually be receiving ESP abilities. All the students are saved and flee the scene.
Saburo, who wasn’t there, still doesn’t know the truth. He transforms into Sannagiman and agrees to fight with Banba. At this point all the Kamen Rider Club members get some short action scenes, except Tomoko. Saburo, who actually had ESP powers, was rejected by his parents and society. Everyone saw him as a monster, except Miyoko, the only current Kamen Rider Club member. She always saw the human in Saburo. As Gentaro is fighting Saburo as Sannagiman, Gentaro eventually decides to cancel his transformation and throws the Fourze Driver into a furnace destroying the belt. He tries to stop Saburo as his senior, his teacher and as his friend.
On the other hand, Meteor is having trouble fighting Hercules Zodiarts. Gentaro runs to the scene, but is unable to transform with a broken belt. Saburo appears as the fully grown Inazuman and saves the day. Hercules is eventually defeated by Inazuman. Saburo reverts back to human form, but he’s standing there naked. His transformation process is so strong it causes his clothes to explode.
After all the fighting, they see Yuki’s space capsule returning to Earth. Everything seems fine, until Eel shows up and takes the Zebar. Â He uses the Zebar shoots an energy beam, through an antenna, at the capsule and causes an explosion. Everyone thinks Yuki is dead, suddenly a light shines down. The light is actually Nadeshiko saving Yuki. She destroys the antenna and goes into her human form, Nadeshiko. Gentaro is happy to see her, and they run to each other and hug.
Eel flees through a warp hole. Gentaro, Ryusei and Nadeshiko chase after him. They end up around Amanogawa High School, and they realize the warp hole brought them 5 years back to the past.
As they are trying to find Eel, they stumble upon Gentaro on his way to school. Future Gentaro borrows Past Gentaro’s Fourze Driver. Â Fourze part ends here.
Wiseman tells Medusa and Phoenix to work together with the Akumaizer, after hearing about their plan to create an infinite amount of monsters. They capture 5 humans and hook them up to a mysterious machine. They 5 of them are all Gates, and with the machine the Akumaizer creates monsters through their Underworld.
Haruto finds out, and attacks the Akumaizer. Medusa and Phoenix decide not to join the fight as they don’t get along with the 3 Akumaizers. Medusa just can’t accept the way Akumaizer do things.
Eventaully the Akumaizer head to the Underworld, Wizard follows them and before the Gate closes Rinko and Shunpei jump in as well. Haruto wakes up from the shock and finds everything very strange. Koyomi and Wajima keep repeating ‘today is Patrine’s birthday.” Suddenly monsters appear and attack 4 kids. Wizard saves them, but then Patrine appears destroys all the monsters and a crowd gathers. The crowd is cheering for Patrine and she receive praise from every direction.
This day is constantly repeating inside Yu Murakami’s Underworld. Yu Murakami is the one who becomes Patrine. Zatan is actually controlling her from the outside. Unless she wakes up the 4 children, Wizard, Rinko and Shunpei will be stuck in there forever. For some reason, Gaara becomes a pastor and holds the wedding ceremony for Yu and Haruto. With the help of Rinko and the 4 children, the mind control is broken from outside.
Haruto fights Gaara and summons Dragon. Gaara transforms into the giant, Gaaraccho. Fights between Wizard and Akumaizer ensues, Patrine is saved and they all return to the real world. But Patrine ends up captured again and the movie leads to Movie Wars Ultimatum.
Koyomi who was left behind actually meets Team Fourze. She gives Gentaro a special ring with Fourze’s face on it. This allows Gentaro to enter the Underworld.
The Akumaizer’s real plan is to use the energy stored inside the Zebar to throw it into the Sea of Hell. Which will cause an overflow of magic which will reach Earth. Humans who aren’t resistant to magic will then die. Akumaizer takes their armored car to flee, and battle fights with bikes occur.
Eventually they reach some cliffs and Zatan summons the Zaiderbeck, a living mech-like creature. With the Zaiderbeck and Zebar, Zatan tries to go to the Sea of Hell, which is in the depths of Underworld. To stop Zatan, Fourze asks Meteor and Nadeshiko for their strength and access Meteor Nadeshiko Fusion States.
Patrine (Yu Murakami) wishes so hard that the Special Rush Ring is created. With this ring, Wizard basically equips Dragon. Together, Fourze and Wizard defeat Zatan.
It is then revealed that the owner of Donuts Shop Hungry’s real name is Yu Murakami. Donuts Shop Hungry’s owner’s, Yu Murakami, Underworld is actually his/her ‘ideal self’. Everything is how (s)he wants his/her life to really be. (S)He actually wants to marry Haruto as the female Yu Murakami. Haruto can’t believe what’s going on.”