The idea of Fate/Zero was proposed by writer Gen Urobuchi who wanted to write a new series under Nasu's guide. Urobuchi explained that 90% of the proposals were accepted by Nasu. During the original visual novel, Fate/stay night, Saber explains she made brief interactions with Kiritsugu Emiya which lead to the creation of the character of Irisviel. As Kiritsugu's wife, Irisviel plays the role of facilitating communication between these two, who do not talk to each other. The distanced and ultimately dark relationship between Kiritsugu and Saber caused by the former's actions in the story led Urobuchi and Nasu to change some early drafts in the story. This was in order to create a more coherent relationship between Saber and Shiro Emiya in the original visual novel as during the finale Kiritsugu adopts the child. Nasu was in charge of the use of magic rather than attempting to use real occultism. The ending of the novels brought Urobuchi difficulties to write as he wanted to distance it from typical stories but in the end decided to follow his own type of writing. During the characterization of the main characters, Urobuchi had no issues writing their ideologies, to the point of finding them as their own individuals.