After nuclear experiments trigger a sudden transformation in the Fumoon, a diminutive yet brilliant humanoid tribe residing on a secluded island, the discovery is met with skepticism except by a select few like Dr. Yamadano and the detective Shinsaku Ban. Alongside the youths Rock, Kenichi, and Kenichi's sister Pichi (known as Pinoko), they bear witness to the Fumoon's advanced intellect. As the Fumoon embark on a mission to save Earth from destruction caused by a cosmic event, including the kidnapping of animals for their journey, a bond forms between one Fumoon named Rokoko and Kenichi. Despite the Fumoon's plan to abandon humanity, Rokoko allies with Kenichi and his companions to construct a spacecraft with the help of Dr. Ochanomizu and Dr. Frankenstein, aiming to offer a chance of escape for a select group of humans.