The story is set in Heroland, a world created by the inventor Ururu where heroes and heroines can all meet. Shimajirou hears that Gaogao-san is in trouble and hurries to help him in the "Dokodemo Sidecar." Using it, he reaches Heroland. There, Shimajirou meets his hero Ratman, but a robot threatens Heroland. Shimajirō and the others must come together and save Heroland.