Mamoru Hosoda stated that this film will be a gender swap of the famous William Shakespeare story "Hamlet", while it will be also inspired by the story of Joan of Arc, Prinzessin Mononoke (1997), The Little Prince, the Dune series, the unmade animated feature adaptation of Barlowe's Inferno by Wayne D. Barlowe and Der König der Löwen (1994).
Mamoru Hosoda has said that this movie is his answer to Der König der Löwen (1994) like how Belle (2021) was to Die Schöne und das Biest (1991).
Hosoda stated the film is not 2D animation or "Hollywood-style CG," and he is aiming for a completely new type of look of animation for this film.
Mana Ashida based her performance of Scarlet on real famous historical warrior women such as Joan of Arc and Elizabeth I.
Mamoru Hosoda has stated that he also took inspiration from famous literature stories such as "The Wasteland" by T.S. Eliot, "Paradise Lost" by John Milton, "The Divine Comedy" by Dante Alighieri and "At the End of the Endless Stream" by Sakyô Komatsu for the inspiration for this movie's story and tone.