Urobuchi had no issues writing the main characters' ideologies. These changes were to create a more coherent relationship between Saber and Shirou Emiya in the original visual novel. 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, including the addition of Kiritsugu adopting Shirou. As Kiritsugu's wife, Irisviel plays the role of facilitating communication between these two, who do not talk to each other. In Fate/stay night, Saber explains she had brief interactions with Kiritsugu Emiya which led to the creation of the character of Irisviel. When starting the project for Fate/Zero, Nasu decided to give Urobuchi complete freedom for Kiritsugu's characterization. Ideas like Saber being lectured by Gilgamesh and Alexander the Great gave him a bigger impact. Writer Gen Urobuchi was pitched a prequel of Fate/stay night by Takeuchi, Nasu was amazed by Urobuchi and had predicted in 2002 while unable to work on Fate/stay night due to illness that Urobuchi would write an interesting story. According to the website Kotaku, Shirou's intercourse with Sakura has become an Internet meme that replaced Sakura's nudity with multiple images. Scenes from the original visual novel that show Shirou having sexual intercourse with the heroines are commonly censored. About a third of the scenario of the future Fate arc (up to the battle with Sasaki Kojiro) was completed at that time, but for several personal reasons, Nasu could not write further for more than ten years. According to Nasu, this version contained elements of 1980s romance and ideas of transformations to world order, while the final version focuses on changes within people and has other purposes for using the Holy Grail. The original idea was limited to the prototype of the Fate arc, where the main characters were the female master and her Servant Saber (the embodiment of King Arthur as a man). The novel Makai Tensho influenced Nasu to write a fantasy story in which famous heroic personalities from all over the world would take part. Artist Takeuchi suggested switching the protagonist's and Saber's genders to fit the game market. In the beginning, Nasu was worried that because the main character was a girl, the story might not work as a bishōjo game. After the success of their first visual novel Tsukihime in 2000, Type-Moon transitioned from a dōjin soft organization to a commercial organization. Nasu set aside the project and went on to found Type-Moon with artist Takashi Takeuchi. This early draft was later embodied in the short original video animation (OVA) Fate/Prototype, which was released with the final volume of the Carnival Phantasm OVA series.
In his early drafts, Fate 's heroine Saber was a man, and the protagonist was a girl with glasses. Kinoko Nasu wrote only one Fate/stay night in college intending Shirou and Saber to be the only couple.