During World War II, Japan had initiated a secret project to develop giant robots as a weapon with hope it would turn the tides against the allies. Shaken by the deaths of his wife and son, Professor Kaneda gets the motivation to successfully complete the 28th Tetsujin, which he named after his son, Shotaro. Many years after the war, young Shotaro Kaneda pursues after the mischievous Murasame brothers. Meanwhile, a giant rocket heads toward Tokyo. Landing in front of Shotaro and the Murasame brothers, the rocket opens and reveals the figure of a giant robot. What secrets does this remnant of a dark past hold? And how will the fate and lives of a country change with it?