Yoshikawa Eiji is the author of a serialisation about Miyamoto Musashi.
I remember reading the version that was condensed into a novel several years ago. How surprised I was to see that mangaka Inoue Takehiko (of Slam Dunk fame) faithfully reproduced it in a manga version.
the same kind of gloomy, introspective, and almost bestial at times, atmosphere from the book is here alright