Tetsuro Hoshino is a young boy born into poverty on Earth, with an overwhelming desire for a mechanical body. His ambition is fueled by the need for revenge against Count Mecha, a villain bestowed with a machine body who hunts humans for sport and was responsible for his mother's death. As an impoverished street urchin, Tetsuro lacks the means to afford such a transformation. Yet, he learns of a planet at the edge of the Andromeda Galaxy where these robotic bodies are distributed freely. To reach this distant world, Tetsuro must secure passage on the Galaxy Express 999, a cosmic railway.
One day, Tetsuro encounters the enigmatic Maetel, who offers him her unlimited-use pass for the Express under the condition that she accompany him as his travel partner. Eagerly, Tetsuro agrees, setting off on a star-spanning adventure with Maetel. Initially, Tetsuro embodies the typical traits of a whiny, immature, and selfish child. Nevertheless, through the myriad adventures with Maetel, the diverse individuals he meets, and the extraordinary sights he witnesses, Tetsuro gradually matures into a strong, young man.
Over time, Tetsuro forms a deepening bond with Maetel. Although their relationship may not be characterized as romantic, they develop a profound connection rooted in love. This journey across the stars not only transforms Tetsuro physically but also molds him into someone capable of empathy, courage, and wisdom, shaping his destiny far beyond what he initially sought.
