Some characters like the Third Exorcist were created as a setup and connected to both Kanda and Alma Karma's backstories. For their story arc, Lavi was supposed to appear but Hoshino found this challenging because it featured multiple characters. As a result, by the end of this story arc Allen abandons the Order so that Hoshino was able to write fewer characters per chapter. Hoshino has gone on to say that she often creates so many new characters across the series, the plot starts to change as it is driven by them. Originally, the setting and plot begin with a more coherent tone, but Hoshino must change them to match the characters' actions and believes it is more exciting to the point they might affect the conclusion. In designing the characters, Hoshino found it challenging as some of them, like Allen and Howard Link, started sharing similarities. To gather research for them, Hoshino uses the fashion magazine "Sou-en" and also asks for her assistant's help.