The Battle Fever saga begins when FBI agent Diane Martin is sent to Japan in pursuit of an assassin. There she encounters the help of Japan's Ministry of Defense special task force, lead by Kurama Tetsuzan Shogun. He and Diane's father, the FBI director, unveil that the assassin is a member of a secret cult known as Egos. The Egos cult, under the leadership of their evil war god, Satan Egos, had already ravaged Western Europe and the Americas and was now spreading into Japan. Diane's father makes arrangements for her to stay in Japan and expose the evil cult, but he is killed before he can return to the US. General Kurama assembles four young agents who had been dispatched around the world for training along with Diane Martin and outfits the team with special battle suits that enhance all of their natural fighting ability. Together they battle Egos as Battle Fever J. Battle Fever J was the first series to use the term Super Sentai and where the heroes must control a giant robot to defeat a monster who itself has grown to a gigantic size. Also, it was Toei's second co-production with Marvel.