How to beat Jakotsu-baba in Nioh 3

Jakotsu-baba is the first major boss in Nioh 3, not including the prologue's Yamagata Masakage. As is typical for the first real boss in any soulslike, Jakotsu-baba is no walk in the park, as I'm sure you've figured out by now.

Not only is Jakotsu-baba a real pain by himself, but he's also inside the Crucible—basically a nightmare realm, where any damage you take also decreases your maximum health. What's already a hard fight is now a true test of skill, as every hit you take sets you even further back.