I found a VERY easy way to kill the Chikage NPC. All you need to do is lure him back to the bottom of the stairs and play around with his AI a bit to get an idea for where he passes that zone of no return before zombie walking back into his arena. It's about half way across the lowest platform in front of the doors. Get him to draw his sword into blood mode, dodge the attacks, and bait him into attacking towards the door. If you dodge around him at this point, you can keep whacking him repeatedly which pushes him back towards the door if your back is towards the staircase. Keep knocking him towards the door, regen stamina, and repeat until he's dead. You can do this even if you have absolutely no attack power on the weapon you're using so use whatever you'd like, as long as it's fast. Let the bleed/poison kill him for you.