Since the fall of the Dark Skull, Doc has constantly suspected that another invasion was coming sending Arnold and Sonya on searches for the new invaders although never finding anything. However, one day, after Doc is kidnapped, Arnold and Sonya find out that an alien empire led by Ryo is planning to take over the world. Also, two other villains have appeared with similar powers to Arnold and Sonya.
Following the collapse of the Dark Skull, Doc has been convinced that another attack was imminent, prompting Arnold and Sonya to investigate for signs of the new invaders, but they were unsuccessful. In the aftermath of Doc's kidnapping, Arnold and Sonya discovered that an extraterrestrial empire under Ryo's leadership aimed to conquer the world. Additionally, two other malevolent entities emerged with powers similar to those of Arnold and Sonya.