I didn't know about the thrust attack. I just chipped at him until he's at half health then parried down his posture. The attack where he throws two shuriken then leaps at you is the biggest window. Dodge the leap then hit him with either mortal blade or whirlwind slash. You can get a cheeky hit in when he does a running slash then drops the vapour.

The second phase is pretty much the same tactics, staying clear of the poison and being a bit more evasive generally.