One easy-to-find upgrade that helps with Nioh 3's Ki Pulse
Pcgamer notes the Samurai style in Nioh 3 is much closer to the methodical, more hardy, planted sword master you'd expect from a soulslike, but it has one defining factor that makes it hard for newcomers: the Ki Pulse. Ki is effectively your stamina, and samurai must press the right bumper on a controller at the correct time during combos to recover Ki; without it combat can feel breathless and awkward.
The Running Water skill can be found in the Hamamatsu Castle Crucible (the nightmare realm you'll enter a short way into the story). Once you reach the point where rock platforms come out of the lava, head into the building to your right, jump over the platforms on this side, kill the enemy that pops out of the mist, and open the large red chest.
There are two other skills recommended while you're in the area that will also come in handy for the Jakotsu-baba boss fight. There is no substitute for mastering the Ki Pulse, even with the Running Water skill.