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.
Since the downfall of the Dark Skull, Doc has consistently believed that another invasion was imminent, prompting Arnold and Sonya to conduct searches for the new invaders, although they never discovered anything. However, after Doc's kidnapping, Arnold and Sonya learned that an extraterrestrial empire led by Ryo aimed to conquer the world. Additionally, two other villains emerged with powers comparable to those of Arnold and Sonya.