Milos Havel is named after two Czech politicians of the series' time - Prime Minister Milos Zeman and President Václav Havel.
At the beginning of Episode 2, "Daily Bread", during the brief scene when Mireille and Kirika are window shopping, one of the stores has the name "Bee-Train". Bee Train is the name of one of the companies that produces the show.
In the English dub Mireille notably doesn't have a French accent and her name isn't pronounced the way it would be in France. This isn't technically an inaccuracy because Mireille's character is Corsican in origin rather than French, and the Corsican language is actually more related to Tuscan than French, and has its own peculiarities.
ADR Director for the English version Matt Greenfield casted his wife Tiffany Grant for the role of Altena after hearing her talking in her sleep about "putting a body on the table."
The show creators described the series to being a gender flipped version of the John Woo film The Killer (1989) with Kirika as Chow Yun-Fat and Mirelle as Danny Lee.