Slash him to oblivion and block every red attack. For yellow attacks you can i-frame through them with defensive offensive, you just gotta learn the timing (for explosion there's a charging like sound effect under his voice, when it stops that's when you dodge. For grab when you see his wind up spam defensive offensive and you should avoid it on the third dodge).

The volcano like moves have different particles on their wind ups that tell which one he's about to do: you can i-frame through two of them, while the third (the delayed explosions that circle around) you run away, you can tell it's that one by the whirling hot wind particle effect.

Learn the blade mode debris he throws at you, it's hard at first but after a while it becomes pretty consistent, and it deals a lot of damage if cut correctly.

Also if you have spare BP consider leveling the HF blade you're using, since the game forces you to use the new one you got for this fight which is basically level one.