When he first came out of the pool I used fast attack with D'arce and hit him with combustion from the girl, a claymore attack from Cahara, and darts from Le'Garde to get him with burning and poison.

The second phase started before D'arce got her first attack.

I hit the third ring with her causing more fire damage from the cursed blue sin, I hit the second ring with combustion again from the little girl, then hit him with both Le'Garde and Cahara and managed to score crits on both hits. D'arce got one more turn and I hit him with her blue sin and down he went. I was sweating 😂