Nicolas Cage wanted to star in the remake if John Woo directed it.
Walter Hill and David Giler wrote a script for a remake of The Killer (1989) as far back as 1992. It was planned to have starred Richard Gere and Denzel Washington.
When Zee is talking to Jenn about her childhood, when she first brings Jenn to her apartment, she retells a story in which an adult asked her what she wanted to be when she grew up. She answered "happy." The adult said she didn't understand the assignment and she responded they didn't understand life. This is a reference to a famous John Lennon quote, in which he says, "When I was 5 years old, my mother always told me that happiness was the key to life. When I went to school, they asked me what I wanted to be when I grew up. I wrote down 'happy'. They told me I didn't understand the assignment, and I told them they didn't understand life."
Finn's nickname for Z, 'Cushla machree' is an Irish term of endearment that translates to "pulse of (my) heart" or "beat of (my) heart". It is derived from the Irish Gaelic phrase 'cuisle mo chroidhe'; that is often used in Irish folk songs and poetry.
Lupita Nyong'o was originally cast as Zee. After the COVID-19 pandemic delayed production, she moved on to other projects and became unavailable, so Nathalie Emmanuelle was cast in her place.