Matsugorou Sawamura is a shamisen player of legendary talent. Upon his death, his grandson, Setsu Sawamura, lost his ability to play. Having lost his beloved sound, Setsu finds himself in Tokyo in search of a new sound to love. Tachiki Yuna, who works at a club, hooks him up with a gig to play there as a warm up act. Setsu imbues the sound of his shamisen with his many thoughts and feelings he has of others, still searching for his own sound and his own feelings.

The legendary Space Sheriff Gavan is hired to capture the Kaizoku Sentai Gokaiger. However, Gavan himself is captured by Ashurada, a Zangyack prison chief and descendant of his old enemy Don Horror, and jailed in the worst prison in the universe. The Gokaigers resolve to rescue the sheriff from the prison and join forces with him to fight Ashurada.

In Kagoshima, in the final days of World War II, an offer of marriage comes to Etsuko Kamiya, who lives with her brother and his wife. The offer comes from Nagayo, but Etsuko is attracted to his friend, Akashi.

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!

Under the impression that they saved the World of Den-O, Tsukasa Kadoya (Kamen Rider Decade) and company begin their journey to the World of Kabuto when they are halted by Sieg who presents them a manuscript that detailed the legendary Oni Conquest with Momotaros' image on it. As this occurred, the Tarōs mysteriously vanish from the DenLiner as they are about to help Kotaro Nogami (Kamen Rider New Den‑O) out with the true threat to their world.

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.

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.

When the Imagin and Kohana take a trip to visit Ryotaro and Airi, they are attacked by the legendary Ghost Train, and onboard are two Imagin and the evil Kamen Rider Yuuki, who is none other than Ryotaro! But when all hope seems lost, a blue DenLiner appears, delivering someone claiming to be Kamen Rider New Den-O! Just who is he, and can he help everyone save Ryotaro and save time once again?