The story is divided in three portions. The Kamen Rider Wizard portion, Kamen Rider Wizard: The Promised Place, taking place after the finale and defeating Amadum. The Kamen Rider Gaim's portion of the film is titled Kamen Rider Gaim: Sengoku Battle Royale!. A battle royale is being held exclusively for the Armored Riders in Zawame City. In the final portion of the film, titled Sengoku Movie Battle, Kamen Riders Wizard and Beast join Kamen Rider Gaim in the alternate world to stop Kamen Rider Bujin Gaim from acquiring the "ultimate power" he seeks.

Gaim: It begins on the planet Kouta and Mai reside. Suddenly a mysterious enemy appears, then heads for their friends back in Zawame City. What is the enemies’ plan to release the curse of the Over Lords and Helheim? This being has even driven Kouta, who has become an existence like-God. Find out how the series continues after the events of the last episode. Drive: A legendary thief, the Special Unit, and Drive are locked in a showdown. How does the Drive Driver (Mr. Belt) fit in to all of this?

Shortly after Shinnosuke Tomari (Ryoma Takeuchi), Kamen Rider Drive, eradicates the Earth of the 108 Roidmudes, he is put on a special assignment to investigate paranormal activity elsewhere in the city. He heads to the temple Daitenkū-ji to speak with witnesses Akari Tsukimura (Hikaru Ohsawa) and Onari (Takayuki Yanagi), but as he is interrogating them, a Gamma appears and steals an Eyecon from the temple, prompting Takeru Tenkūji (Shun Nishime), Kamen Rider Ghost, to fight it, even though to Shinnosuke it seems that Kamen Rider Ghost is fighting no one at all as he cannot see the Gamma

Movie War Mega Max featured the first seven Kamen Riders (Kamen Rider 1, 2, V3, Riderman, X, Amazon, and Stronger) to commemorate the franchise's 40th anniversary. Trailers for the film shown during airings of Fourze also showed the return of Kamen Rider Double as well as a new form for Kamen Rider OOO. Unlike previous Movie War films, where they were divided into 3 segments, Movie War Mega Max is divided into 5 parts. Like previous Movie War films the secondary Kamen Rider of Kamen Rider Fourze, Kamen Rider Meteor, made his debut in the film.

The first part is the Kamen Rider Fourze’s place five years after the events of the series. Gentaro is now a teacher at Amanogawa High as well as the Space Kamen Rider Club’s new academic advisor. However, a new school club called the Monster League, comprised by a group of psychic children led by Saburo Kazeta, which is supported by a mysterious man named Kageto Banba. The second part is Kamen Rider Wizard’s portion, where Haruto enters the Underworld of an unknown Gate to investigate the mysterious occurrings of monster appearances. He then runs into a young woman named Yu Kamimura who can become Belle Mask Poitrine and can use magic like him. The third and final part of the film is Movie War Ultimatum. The three Akumaizer from the Underworld to plan to invade the land of the living. Kamen Riders Wizard and Fourze must fight to stop the Akumaizer and their Monster Army.

Confronting a mysterious enemy, the Pteranodon Yummy, Kamen Rider W receives aid from Ryu, who has infuriated Akiko by being too busy to attend her wedding! Akiko demands to know why he even became a Kamen Rider in the first place and the Pteranodon Yummy as it uses the Memory Memory on her to give her the answer to her question. Meanwhile, at the Kougami Foundation, Kousei Kougami talks of the most avaricious man in Japan, Oda Nobunaga, whose final resting place was found. With Doctor Maki overseeing the process, Kougami commissions the creation of a Cell Medal homunculus based on Nobunaga himself. Later, Kamen Rider Core begins to destroy the area as Kamen Riders OOO and W team up to fight the enemy. However, Kamen Rider Core proves too powerful and the two go underground to destroy the Gaia Memory’s source of power to even the odds.

Serving as the true ending to Kamen Rider Decade and revealing the origins of Kamen Rider W, this movie is split into three parts. In "Kamen Rider Decade: Final Chapter", Tsukasa Kadoya fully embraces his title as the Destroyer of Worlds. In "Kamen Rider W: Begins Night", Shotaro and Philip recount the night on when it all began. Elements of both parts converge in the movie's final part, "Movie War 2010" as our heroes fight the forces of Super Shocker.

Geats, Revice, and Ryuki wage a fierce battle royale that transcends beyond the Heisei and Reiwa eras.