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.

Divided into three acts, the first act is about the Zenkaigers dealing with a new Kashiwa Mochi World and Zocks declares himself as "Kashiwa Mochi King", the ruler of Zenkaitopia?! In the second act, it's been a year since Taro left and the five companions continue to fight as a team with Jiro as their leader. Taro later regains his memories, only for his companions to ask him to leave the Donbrothers. In the final act, an incident caused the two worlds to connect, thus a full-throttle miracle battle between the two Super Sentai begins!

The year is 2021 and the world is in a state of chaos and fear. The ancient king OOO has come back to life after 800 years of dormancy. As the Kougami Foundation mounts a human resistance, Eiji Hino returns to Japan, believing he has at last found the means to revive the Greeed Ankh...

Eiji Hino returns to Japan and delivers some shocking news to Hina...

While testing the Birth X Driver, Shintaro Gotou is shunted into a parallel world filled with many familiar faces in unfamiliar places. Can he master the secrets of the Birth X Driver and return home?

A film crew from a small video production company arrives at an abandoned factory in a remote suburb. Although it is a low-budget movie, it was filmed in a large abandoned factory with a creepy atmosphere. Harawata Man was sleeping. After waking up from his sleep, Harawata Man succumbs the film crew one by one to the insane bloodbath.

Leading an expedition in Germany, Kougami unseals the resting place of one of the alchemists that created the Core Medals in an effort to retrieve a set of lost Medals. However, upon the seal being undone, millions of Cell Medals erupt into a tower while creating a magical barrier that causes parts of Japan to flip over. As the alchemist reveals her plans to become a new OOO, Eiji and his friends are thrown into the past and must find their way back home and stop the alchemist before she destroys the world!

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.

Having finally taken the burden to becoming the true OOO, Eiji fights to prevent Doctor Maki from realizing his "perfect end" while working to reach his ultimate desire of being there for others and having others be there for him.