After a horrific car crash, Dr Tenma lost his beloved son Tobio. Out of grief, he built a robotic son named Astro as a replacement; but soon after, Dr Tenma had the boy deactivated and put into a deep sleep. In the present, the scientist Dr O'Shea finds Astro and risks everything to reactivate him, train him to be a hero of justice, and raise him to be a functioning member of society. Amidst the prejudice of humanity, the pacifistic Astro will promote peace, battle the forces of injustice, and attempt to bridge the gap between humans and machines.