$10 million budget necessary to finance it, Berman put together a team of at least a dozen executive producers. Spike Jonze boarded the project as an executive producer in October 2020 after the film's premiere. Oda credited Jonze's Her (2013), a film tackling similar themes of humanity and vulnerability, as a major inspiration for Nine Days, taking notice of Scarlett Johansson's performance as Samantha in the film: "She's almost like a soul ... finding love and all those emotions so dramatically." Casting Winston Duke read the screenplay after working on Us and was immediately interested in its depiction of mental illness and depression. Duke sat down with Oda for a meeting, which turned into a four-hour conversation about various topics ranging from filmmaking to content they both enjoyed to a discussion about life as an immigrant. As Oda described it, "It was almost like, I don't know, love at first sight. It was just amazing to see that I could trust this guy so much. I had a feeling that he has this big heart for humanity inside him." Though the lead role was originally set to be played by an Asian actor, Duke got the part the day after the meeting. According to Duke, the film's title is a reference to the funerary tradition practiced in the Caribbean known as the nine nights, where a person is mourned for nine days because it takes their spirit nine days to say goodbye. On June 7, 2019, Duke, Zazie Beetz, Bill Skarsgård, Benedict Wong and David Rysdahl were announced to star. Beetz described her character as having a "childlike wonder", living in the present and confronting her issues instead of ignoring them like Will. Wong described his character as a romantic about life, eager for company but alone. To prepare for the role, Wong isolated himself from other people: "I locked myself up in a room ... [and] I didn't talk to anyone, solely just to have personal isolation. And when I came out, I wanted human contact, so that was like Kyo who would walk off into the dead of night, and no one knows where he goes." In August 2019, Tony Hale joined the cast. Hale described his character as a jokester who wants to have a good time. He categorized Arianna Ortiz's character as a romantic and Rysdahl's character as sensitive, stating that "there was a risk that