Like the first two Movie War films, Movie War Ultimatum is split into three parts. 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. The rest of the original Kamen Rider Club members went their separate ways: Yuki becoming an astronaut, Kengo becoming a graduate student at Kyoto Space University to research Cosmic Energy like his father, Miu becoming a model, Shun becoming a professional football player, JK working for a magazine, Tomoko as a novelist, and Ryusei becoming an Interpol agent with Inga Blink. However, a new school club called the Monster League, comprised by a group of psychic children led by Saburo Kazeta who becomes a mutant known as Sanagiman, threatens the school. The Monster League, in turn, is supported by a mysterious man named Kageto Banba who possesses a Zodiarts Switch.
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 by using a Monster Army. Kamen Riders Wizard and Fourze, along with the help of Kamen Riders Meteor, Nadeshiko, OOO, Birth, Double, and Accel, must fight to stop the Akumaizer and their Monster Army.
繼前作《假面騎士Fourze THE MOVIE 大家的宇宙來了!》加入東映系列的其他特攝作品，假面騎士以外的英雄共同演出後，本作同樣加入了《閃電人》(日原文《イナズマン》) 、《伏魔三劍俠》(日原文《アクマイザー3》) 和《美少女假面Poitrine》(日原文《美少女仮面ポワトリン》)三大特攝作品的主角演出。
本作把《假面騎士W》、《假面騎士OOO》、《假面騎士Fourze》、《假面騎士Wizard》中的主角和二號騎士及怪人實行大集結，同時前作《假面騎士×假面騎士 Fourze & OOO MOVIE大戰 MEGA MAX》中登場的假面騎士Nadeshiko亦會回歸。
