"Chiisana Kyōjin Microman" is a science fiction anime series that revolves around the adventures of a group of tiny humanoid beings known as Micromen, who hail from the planet Micromini. The Micromen, standing only a few centimeters tall, possess advanced technology and superhuman abilities, which they use to protect their world and, eventually, Earth. The narrative begins when the Micromen's home planet is threatened by the evil Emperor Zaltz and his army of robots. Facing imminent destruction, a group of Micromen escapes to Earth, where they encounter a young boy named Daichi Yamagishi.

Daichi, an ordinary elementary school student, discovers the Micromen after they crash-land near his home. He quickly forms a bond with them, particularly with their leader, Microman, and his companions, Microsaber, Microlaser, and Microknight. Together, Daichi and the Micromen form a team dedicated to defending Earth from Emperor Zaltz's forces, who have followed them to the planet. The series explores their battles against Zaltz's robotic minions, as well as their efforts to adapt to life on Earth while keeping their existence a secret from the human population.

The Micromen's advanced technology allows them to transform into larger, more powerful forms, enhancing their combat abilities. They also utilize specialized vehicles and weapons, such as the Micromachine, to engage in high-stakes battles. Throughout the series, the Micromen face various challenges, including infiltrating Zaltz's strongholds, rescuing captured allies, and uncovering the true extent of the emperor's plans. The narrative balances action-packed sequences with moments of camaraderie and growth, as Daichi and the Micromen learn to trust and rely on one another.

As the story progresses, the Micromen's mission expands beyond mere survival. They uncover deeper mysteries about their origins and the true nature of Emperor Zaltz's ambitions, which threaten not only Micromini and Earth but the entire universe. The series culminates in a climactic showdown between the Micromen and Zaltz, with the fate of both worlds hanging in the balance. Through teamwork, courage, and ingenuity, the Micromen and Daichi strive to overcome overwhelming odds and secure a future for their respective civilizations.