The language depicted in texts/captions throughout the film is Esperanto, an artificial universal language that was created to be spoken internationally, and in which Kenji Miyazawa was deeply interested. The film even holds a title in Esperanto ("Nokto de la Galaksia Fervojo").
The wireless operator picks up fragments of a cryptic message which is later discovered to be parts of "Nearer, My God, To Thee" (Hymn #306). The express later picks up three people from a shipwreck closely resembling that of the Titanic. That hymn was one of the last the ship's band played as passengers filled the lifeboats. It is uncertain in what hymnal it is listed as #306; however, there were 306 bodies recovered from the disaster by the cable ship MacKay-Bennett.
The main characters are depicted as cats, with some humans serving in supporting roles. According to director 'Gisaburô Sugii', this was a necessary move learned from experience - having adapted most of Kenji Miyazawa's stories into manga, he saw that making the characters human made the stories more tangible, but less unreal and magical and thus limited their appeal. Making the characters anthropomorphic animals, on the other hand, maintained the epic and surreal scale of the story.
The film is based on an unfinished children's novel by Kenji Miyazawa. He started work on the novel in 1924, and kept polishing the work until his untimely death in 1933. In adapting the film, the novel's unfinished portions (mostly the middle sections) were handled by writer Minoru Betsuyaku.
The main characters are portrayed as cats. Ironically, Kenji Miyazawa was said to have disliked cats.