I dont really care for Genichiro as a character, but the way this boss fight was built up is magnificent. First, the game sharpens your deflect/parry game with the Ashina Elite miniboss, who deals tons of damage. Immediatly after, you finally have that long awaited confrontation with the one big nemesis you've been chasing so far. His attacks are a lot slower and forgiving than that of the Ashina Elite, but he gives you very few openings. His movepool is large, but they're all telegraphed very well. Fighting him feels familiar, as it should, and clashing head on is encouraged by a posture bar that both increases and decreases quickly, rewarding you with a quick finisher should you do well enough.
So much thought has went into it.