It is also a biography, somewhat incongruously narrated by a sedate Keanu Reeves.

The director, Steven Okazaki, talks to Mifune collaborators like the actress Kyoko Kagawa and Kanzo Uni, a sword-fight choreographer whom Mr. Mifune is said to have “killed” more than 100 times. The actress Terumi Niki discusses how Mr. Mifune coaxed performances out of his co-stars during the filming of “Red Beard.”

But the film’s richest insights are into Mr. Mifune’s longtime partnership with Akira Kurosawa. As the film tells it, that otherwise exacting director accorded his apparently fearless star unusual leeway. Teruyo Nogami, Kurosawa’s frequent script supervisor, recalls how in the violent finale of “Throne of Blood,” the archers shooting arrows at Mifune were college students and not especially good shots.