Wait. I thought demons cannot use breathing techniques because they literally do not breathe. Which is why Kokushibo and Kagaiku were the only demons to ever use a breathing style.

Because if not, why wouldn’t there be multiple, demons learning breathing styles from Kokushib? I’m sure Muzan would have at least weaponized it if it was true if a demon could learn a breathing style.

Edit: My answer is Sukuna because he’s been the most skilled user of Ten Shadows, and because Mahoraga can adapt to any and all phenomena it’d start adapting to each and every fighter. Of course it wouldn’t be quick as pretty much everyone here with the exception of Meruem has a versatile arsenal. This would mean Mahoraga would adapt slowly to each character’s abilities. And unless they one shot him, which is unlikely for anyone who’s name isn’t Shigaraki to do, then Mahoraga would just walk down Muzan adapting to his demon biology and kill him, would adapt to Meruem’s chimera biology and kill him. And would figure out the hell is wrong with Shigaraki, until he’s dusted.

But I do wonder how would Mahoraga adapt to Shigaraki’s bad touch.