Prior to the role of Dawn being cast, Sarah Michelle Gellar suggested they take a look at Michelle Trachtenberg. Dawn was originally conceived to be 12 years old, but after Trachtenberg was cast, the writers raised the character's age to 14. However, the first few scripts were still written in the voice of a 12-year-old. Before being cast, Trachtenberg, a fan of the show, had written a letter to Real Me (2000) that suggested how she could become a character on Buffy. The character of Dawn was also originally intended to have the power to speak to the dead, or to be able to move objects with her mind. These powers were later dropped.
David Fury says he was "given a lot of freedom to develop Dawn" as her background was completely unknown. He set up her relationships with other characters, such as Willow's status as Dawn's "favorite aunt", and provided additional backstory that - although not necessarily appearing in the finished script - "infused her character in future episodes."
Michelle Trachtenberg has been added to the opening credits, marking the shortest period in which an actor goes from a guest credit to a main character (only one episode, with Dawn's debut appearance being at the very end of Buffy vs. Dracula (2000)).
First appearance of Giles' red BMW, replacing his Citröen which Spike wrecked in S4's A New Man (2000).
Dawn's description of Willow and Tara's relationship, implies Joyce knows about its romantic/sexual nature; she was oblivious to their sexual orientation in the previous episode Buffy vs. Dracula (2000).