Mishima: A Life in Four Chapters is an art-house biography about Yukio Mishima, celebrated Japanese writer, who bears resemblance to Paul Schrader's earlier character Travis Bickle (Taxi Driver): both of them are lonely people searching for their place in their society and when they realize that world doesn't need them, they try to destroy their surrounding universe.
If you want to learn about life of Mishima, then you won't find a lot of information here, because it shows that he didn't live a very interesting life (except for his final day), but if you want to understand his personality, then it is the best movie of its kind, as most of the movie is adaptation of his novels and also provides a guide to his thoughts. This movie shows that Mishima was a person, who witnessed the fall of Japanese culture, which he was very fond of and with his final act he tried to save traditions and prove to himself that he is a real warrior, but he realized that as a person he was just a man with no power to change the events.