The fact that Musashi free climbed a mountain on a badly infected foot is insane. He is so determined and rightfully skilled in anything he takes up, it's truly inspirational.
Also him realizing just how far the gap in strength he has between himself and In'ei and Sekishusai and accepting of it is a good character touch for him. In'ei's words of not thinking about true strength unless you're truly strong is resonating with Musashi well. As well as Sekishusai's words of invincible being merely a word; Musashi realizes how such a trivial thing like that is so irrelevant to the whole grand scheme of life.
This chapter up till now also had some of the best artwork this series has to offer and I know it gets even better. But this chapter was pretty special.