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.

Kosei Tomita
as Shunsaku Ban (voice)

Junichi Takeoka
as Rock (voice)

Nachi Nozawa
as Black Jack (voice)

Mari Shimizu
as Astro Boy as "Adam" (voice)

Hisashi Katsuta
as Professor Ochanomizu as "Dr. Narzenkopf" (voice)

Yoshiko Ohta
as Princess Sapphire as "The Empress of the Mu Empire" (voice)

Chikao Ohtsuka
as Duke Red as "Director Credit" (voice)

Kaneta Kimotsuki
as Hosuke Sharaku (voice)

Mami Koyama
as Chocola as "Milly" (voice)

Kouichi Chiba
as Don Dracula as "Dondora" (voice)