What is the move this guy is using in this fight?

Spoiler warning for a boss fight in the game, don't watch the video if you haven't fought Ifuu and Burai yet.

Video

What is the double hit move this guy uses on both of them at the same time? I just finished this fight and that would have been cool to pull off. It's not a double-exhausted-stamina move, I checked. So what is it exactly?

I start the video at the instance of where the move happens. Also I never parried them like that as they never came at me without their charged move where they spin and hit each other after the parry, so I'm guessing that's why? It does so much damage, woulda been nice to pull off a few times lol.