In 2015 A.D., Dr. Yamanoue, Secretary of the Science Ministry, dedicates himself to assembling an Android robot on an artificial island. He intends to live with the robot as his own son. However, the robot suffers from a deficiency in its electric brain. Dr. Yamanoue concludes that Dr. Kawashimo's assistance is essential to correct this defect. Although they are friends, they are rivals in both private life and scientific study. Dr. Yamanoue is highly jingoistic and views the robot merely as one of his strategic weapons. 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 arrival, 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 up onto a building. When he sees a glint of moisture in Miri's eyes, he experiences a mysterious feeling in his mind. He then asks Dr. Yamanoue what it is. He is told that it is a tear shed by a weak girl, but that a strong man never sheds one. One day, the electric brain of Fainton, another robot, malfunctions. Consequently, Fainton goes on a wild rampage, plunging the island into crisis. When 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 large hole. Following her lead, Mars also carries a sheet of iron to make repairs. Finally, they rescue Dr. Yamanoue and Dr. Kawashimo from being washed away by seawater. Miri is a robot created by Dr. Kawashimo. Mars learns how to cry and how to perform a kind deed.