 The setting, mythos and landscape were primarily inspired by the folklore of Northern Europe, while other elements drew from Japanese-style revisionism. According to Shiba, multiple elements of the story and world were created to be dark, sad and serious in tone, in contrast to the likes of Dragon Quest and Final Fantasy. One of the core narrative threads, involving romantic feelings between siblings, was inspired in Yoko's mind by the anime series Sister Princess. Another series that inspired the team was Neon Genesis Evangelion, with a comparison being drawn between them due to a shared trait: while having standard premises, darker narrative elements were hidden in its content. The central narrative theme was "Immorality", which was mostly demonstrated by writer Sawako Natori through the characters. Multiple endings were made because Yoko was told that the game would not have a sequel. The characters' stories were created by Yoko and Iwasaki, who independently created the character backgrounds: Yoko took charge of Seere, Leonard and Arioch, while Iwasaki was involved in developing Verdelet, Inuart and Caim. In an interview concerning her role in the game, Natori admitted to feeling embarrassed by her writing when hearing Sota Murakami and Natsuki Yamashita, who voiced Seere and Manah, speak their lines.
