Heavy Metal L-Gaim is an anime television series, begun in 1984, which was directed by Yoshiyuki Tomino. Its characters and mecha were designed by Mamoru Nagano, who would later go on to create The Five Star Stories. Heavy Metal L-Gaim takes place in the Pentagona System, a solar system made up of five planets. Oldna Poseidal, the legendary emperor from the planet Gastogal leads his 24 Temple Knights from planet to planet until all have fallen under his control. His final victory is on the planet Mizum in 3975 when he defeats Kamon Walha V, ruler of the Yaman Clan. Kamon hides his heir, Kamon Myroad on the planet Mizum with the legendary white mecha, L-Gaim. Fifteen years later, now grown up and known as Daba Myroad, he leads a rebellion to free the planets of Pentagona from Poseidal's grasp.

Hiromi Oka, a first-year student at West High School, joins the tennis club admiring Reika Ryuzaki, aka Mrs. Butterfly, and senior Todo. She is a complete beginner, but as soon as she joins the club, the devilish coach, Munekata, sees her talent.

High school freshman Hiromi joins the tennis club because of her admiration for Ryuzaki. Ryuzaki is a senior, who's the best tennis player on the team and also nicknamed "Ochōfujin", ("Madame Butterfly"), because of her elegance on the tennis court. However, the new coach, Jin Munakata, wants the inexperienced Hiromi to play in a forthcoming tournament.

The plot of Marine Express can be described in two parts. The first part focuses on the people boarding the train and the problems they encounter on it. The second part takes place after the train has stopped at its half-way point, an island that used to be home to an ancient civilization millennia ago and has its fair share of secrets.