These traits of yakuza itself defined the movie industry in Japan of the 60-70s. As it existed historically there was no need to make up stories. Life itself pulls the trigger of the movie genre boom. Roughly speaking, that era was the time of something like a "new Japan wave", because all new waves started like this. It pushed back boring classical movies by Akira Kurosawa, cliched stand shots by Yasujiro Ozu. New wave led to real creative upheaval. That was new Japanese individualism, free of the traditional boundaries.
Yakuza-eiga (jap. ヤクザ映画, literally – gangster movies) is a genre of movies with yakuza theme. It began to emerge in the early 1960s and continued to flourish until the 1970s. The genre gained additional impetus by making the characters suffer a constant conflict between their duty towards their yakuza brothers and their own human nature. Eventually, the leading actor of such films would abandon his humanism to exact violent vengeance upon clans of evil yakuza, usually perishing in the end, having slaughtered every one of them.
On the «КЛАССИКА ЯПОНСКОГО КИНО: ЯКУДЗА»
festival The Art of The Cinema («Искусство кино»)
made a retrospective of 3 movies: A Colt Is My Passport ('Koruto wa Ore no Pasupōto', 1967)
directed by Takashi Nomura; Violent Cop ('Sono otoko, kyōbō ni tsuki', 1989)
, also known as 'Warning: This Man is Wild', directed by Takeshi Kitano and starring him, and Tokyo Drifter ('Tōkyō nagaremono', 1966)
directed by Seijun Suzuki.
These are good examples of 60-70s genre movies.
There is one interesting detail that is worth mentioning. The Nikkatsu studio, Japan's oldest major movie studio, was known for modern yakuza films inspired by Hollywood gangster films. 2 out of 3 movies in the festival list are made in Nikkatsu
(Tokyo Drifter and A Colt Is My Passport). And, as a result, you can see how these films have been soaked in that special style, humor, and skepticism, borrowed from Hollywood. Those movies are not "serious", you can watch some moments with a tender smile or almost laughing out loud.