Kigoro Ikushima and Kinuyo Tanaka come to Chôjûrô Kawarasaki, seeking his help in avenging their father. His death was at the hands of a follower of the Gan school, and he fights them regularly, alone against a dozen of them, when they're not trying to ambush him. He kills them all, of course, The real Musashi wrote a book on swordplay and another on the philosophy behind his style of swordsmanship, and won more duels - 61 in total - than anyone else in Japanese history. Under the direction of Kenji Mizoguchi, he spouts bits of philosophy and hacks people to death when he isn't carving statues of the Buddha,
It's a potboiler distinguished by the careful set design and imagery that Mizoguchi usually gave his movies. This was produced as part of a multi-media campaign that the Japanese government was running, extolling the glories of bushido; the credits make mention of a series of articles that was running in the newspapers.
Musashi was a seminal character in the samurai cult, but the 55 minutes this film takes doesn't offer more than a gloss on the actual legend. Inagaki would direct a three-movie version in his SAMURAI trilogy. This is simply a propaganda film, despite the nice touches that Mizoguchi was incapable of not offering.