>>18070101 (OP)
Sort of the last samurai before the Edo period began and he wrote a book.
I think it helped he was a lot like Diogenes in many respects. There's that cynical disregard for tradition and "fairness" of society's expectations. He'd often show up extremely late to duels and win and say he won because he was the superior strategist because his opponent would be waiting hours for this fucker only for him to show up late and well-rested while his opponent is psychologically miffed. Then that one time he kills the Yoshiokas, he actually shows up earlier this time and ambushes them.
Also contextual, samurai duels were pretty rare. Before Musashi you had the Sengoku Jidai and most of the warriors had better things to do than throw away their lives in honor duels. Once the Shogunate was established and peace started, samurai began getting bored and honor duels were more of a thing, but very rarely duels to the death. The reasoning being even that lords had better things to do than have their valuable and skilled retainers throw their lives away for nothing.
So you had a guy who reportedly won 60+ formal duels, which are all pretty rare, and some of them to the death, even more rare, and the samurai after him were even more pansies and became mostly bureaucrats. So during the Edo Period, this guy sort of became the William the Marshal of his time. Legendary feats and accomplishments that hyped him up and later eras had no real way of matching.