This boss is located in the entrance of the burning main hall in Hirata Estate, past the pond.
How to defeat this boss?
This boss has several henchmen who will instantly join the battle as soon as you aggro any of them. The best way to deal with him is to take time isolating and assassinating his men. This way, you can concentrate on fighting him in a one-on-one battle. There’s also a friendly NPC standing by the grassland in front of the estate who will help you in battle but he can die quickly if he gets flanked or surrounded. To maximize his use, you have to lessen the threats around him.
First, enter the building to the left and take out the two enemies there.
While in the same room, peek outside a bit, just enough to get Jozou’s attention. Don’t let his detection meter turn red; just a full “suspicious” yellow gauge is enough. This will force him to leave his position by the main hall’s stairs.
After Jozou leaves, you can now sneak through using the walkway connecting to the main hall entrance. Make sure Jozou turns his back so you can assassinate one of the shield-wielders by the entrance without aggroing him.
From there, if there are enemies who get suspicious, fall back to the walkway and even lure them there. Just avoid directly aggroing Jozou while you work on whittling down his men.
Repeat this until there’s only him and at least two more enemies left, preferably an archer or swordsman. This way, you can safely perform a stealth deathblow on him.
Quickly kill the archer then lure Jozou and the last swordsman to the allied NPC. Prioritize taking out the swordsman so you two can gang up on Jozou. Remember to attack aggressively while your ally is distracting him then block/evade if ever he turns his attention to you. Your ally NPC will aggressively attacking him as well, interrupting some of Jozou’s attacks and give you opportunities to land free hits.
Even if you manage to land a stealth deathblow on Jozou and with the help of the allied NPC, don’t let your guard down. Jozou can imbue his weapon with poison and can spray poison mist in a wide, short-range in front of him.
Jozou’s normal swings can be blocked but they do deal heavy posture damage. Due to the wide arc of his sword swings, it will be challenging to get the timing of deflecting these attacks. As long as the friendly NPC is still alive, you can take the opportunity to hit Jozou with powerful combat arts or charged attacks to finish him off.