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!

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".

Kamen Rider OOO Allstars: The 21 Leading Actors and Core Medals (ネット版 仮面ライダーオーズ　ALLSTARS　21の主役とコアメダル, Nettoban Kamen Raidā Ōzu Ōrusutāzu: Nijū-ichi no Shuyaku to Koa Medaru) is 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.