In the distant future, humanity has discovered a method to achieve immortality by buying mechanical bodies, yet this path to eternal life is prohibitively costly. Tetsurou Hoshino, a destitute boy, longs to secure a ticket for the Galaxy Express 999—a train that traverses the cosmos—because rumor has it that passengers can receive a mechanical body without charge at the journey's end. However, when Tetsurou's mother is shot dead by the villainous cyborg Count Mecha, all hope appears to vanish. Tetsurou is subsequently rescued from imminent death by the enigmatic Maetel, a tall blonde woman who bears a striking likeness to his mother. She provides him with a ticket to the Galaxy Express on one condition: they must travel together. Consequently, Tetsurou embarks on his voyage across the universe, visiting many unique planets and experiencing thrilling adventures, in the hope of finally obtaining what he desires most.