From Henshin Justice:
Gokai Red has a new Ranger Key. For some reason, it’s Kamen Rider OOO’s Tajadol form. Decade’s new card, an unidentified Gosei Card. Marvelous and Tsukasa, will be fighting hand-to-hand combat out of suit, but the highlights are when they transform. To back up OOO, Birth and Birth Prototype joins the battle. However, Gokai Red and Biohunter Silva’s attacks are simply too much! Great Shocker’s new base, is now located inside Crisis Empire’s battleship, Crisis Fortress.
The villains who have previously attempted to eradicate all Riders have now become Tsukasa Kadoyas’, Kamen Rider Decade, underlings. Early on in the movie, Gokai Red Gokai Changes into various Red Rangers while fighting the Legendary 7 Riders. The Gokaigers can’t believe that Captain Marvelous decided to lead the Great Zangyack into fighting the Kamen Riders. They are determined to stop the war. Decade, Ryuki and Blade obtained 3 mysterious Gosei Cards. What is the source of these cards and what will these cards do!?