In 2015 A.D., Dr. Yamanoue, the Secretary of the Science Ministry, dedicates himself to assembling an Android robot on an artificial island, intending to live with it as his own son. However, the robot has a defect in its electric brain. Dr. Yamanoue concludes that Dr. Kawashimo's help is essential to correct the faulty brain. Although they are friends, they are rivals in both private life and scientific study. Dr. Yamanoue is extremely jingoistic and views the robot solely as a strategic weapon. In contrast, Dr. Kawashimo is a pacifist who devotes his affection to robots.
At Dr. Yamanoue's request, Dr. Kawashimo hurries to the island, bringing his pretty young daughter Miri with him. Upon arriving, Dr. Kawashimo installs the electric brain into Jet Mars, a robot boy. Thus Mars comes into the world. Everything is new to Mars, and he does not know what is good or bad. The next day, he lifts Dr. Kawashimo and Miri onto the building. When he sees a glint of moisture in Miri's eyes, he feels a mysterious sensation in his mind. He asks Dr. Yamanoue what it is and is taught that it is a tear shed by a weak girl, but a strong man never sheds them.
One day, the electric brain of Fainton, another robot, malfunctions. Fainton goes on a wild rampage, plunging the island into crisis. Seawater floods the facilities through a large hole made by Fainton. Mars stands in amazement, at a loss for what to do. Just then, Miri exhibits her ultra ability and covers the big hole. Led by her, Mars also carries a sheet of iron and helps with repairs. Eventually, they rescue Dr. Yamanoue and Dr. Kawashimo from being washed away by the seawater. Miri is actually a robot made by Dr. Kawashimo. Mars learns how to cry and how to perform kind deeds.