According to Keanu Reeves, filming was first done in Japanese for the sake of the supporting cast, and then filming was done in English.
Carl Rinsch clashed with Universal over the final vision of the film. Universal wanted to make an effects-driven fantasy blockbuster akin to Avatar (2009) or The Lord of the Rings, while Rinsch envisioned the film as more of a drama, such as Il gladiatore (2000), or Le crociate - Kingdom of Heaven (2005).
This is the seventh cinematic adaptation of the 47 Ronin incident, after I 47 ronin ribelli (1941), Chûshingura (1958), Chûshingura (1962), Akô-jô danzetsu (1978), Shijûshichinin no shikaku (1994), and Saigo no Chûshingura (2010). This is however the first Hollywood cinematic adaptation.
The film's budget ballooned to $175 million because of complex re-shoots and a lengthy post-production period. While not a success in cinemas, it did well on VOD, DVD, and Blu-ray.
The character of Kai seems to be patterned after Minamoto Yoshitsune, a twelfth-century warrior said to have been trained in martial arts by Tengu.