The casino in the opening scene is named Watanabe Casino. This is a nod to Shin'ichirô Watanabe, the director of the original anime.
The characters of Asimov and Caterina are based on Antonio Banderas and Salma Hayek's characters in Desperado. As a nod to this, the El Rey bar is a recreation of the bar from this movie. In addition, the name "El Rey" features frequently in Robert Rodriguez features, such as "Planet Terror" and "From Dusk Till Dawn".
The opening sequence was partially based on the one from Cowboy Bebop: The Movie (2001). One major difference is that the event takes place in a casino, while in the film, it takes place in a shop.
The tequila bottle the El Rey bartender puts on the bar is Mariachi brand. The El Rey bar is based on the bar from the movie Desperado, which is a sequel to El Mariachi.