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...

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!

Confronting a mysterious enemy, the Pteranodon Yummy, Kamen Rider Double 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… 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. Kamen Rider Core begins to destroy the area as Kamen Riders OOO and Double 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.

A series of net movies that were released by Toei to promote the Kamen Rider OOO summer movie, "Kamen Rider OOO Wonderful: The Shogun and the 21 Core Medals".

Eiji and Ankh team up with Kotarou and Momotaros as they travel back in time to 1971 aboard the Den-Liner to stop three Mole Imagin. But Ankh’s desire to obtain Core Medals while in the past sets off a chain of events that alters the 40-year history of the Kamen Riders by allowing Shocker to take over the world. It’s up to OOO and New Den-O to restore the timeline!