To protect Earth from alien invaders and their colossal monsters, Dr. Kishida follows the classic mad‑scientist trope and builds a giant robot, ARIEL, designed as the ultimate feminine fighting machine. Unfortunately, his granddaughters refuse to pilot it, claiming they have more important things to do, like studying for college entrance exams, than becoming teenage superheroes. Meanwhile, the alien forces believe Earth, with its lush, peaceful environment and relative defenselessness, should have surrendered long ago. Yet the conflict erupts, and the battle for the planet begins.