After witnessing his mother's death and being left for dead by Count Mecha, ten‑year‑old Tetsuro Hoshino is awakened by a mysterious woman named Maetal. In exchange for his company alone, Maetal offers him a chance to travel on the legendary Galaxy Express 999. Those who reach the end of the line aboard the train are said to receive a mechanical body, granting them immortality. Impoverished and alone, Tetsuro seizes the opportunity and joins Maetal on a cosmic quest. As the Galaxy Express 999 journeys through our solar system and beyond, Tetsuro finds himself drawn into a perilous universe where danger lurks at every stop.