The story opens with a spaceship attempting to return home, crash-landing on a dying planet. The powerful and unknown beings operating the vessel cause a surge of energy that revitalizes the planet. In a remote part of the forest, the protagonist, Popo, resides with his mother and various insects. Popo's goal is to grow stronger, find his father, and become the new Guardian of the Forest. However, an eerie mist blankets the forest and a nefarious figure accuses Popo's father of being a troublemaker. When Popo returns home, his mother has transformed into a hybrid plant-human creature. Convinced that only his father can remedy the situation, Popo teams up with Mushiking, a beetle king who aids him on his journey. Despite opposition from antagonists and colossal beetles, Popo persists and discovers his fate as the Savior of the Forest.