Primordial Essence!

When Noah had met the Sword Kings of the Consummate Sword Expanse before, they had repeated to him multiple times that the 'Will of the Sword Emperor' would always be followed.

He thought this was mere fanaticism to the Sage of their Ancient Power, but he now realized it was something much grander as he felt the power of the Sage for himself!

He was releasing such dominating strength that Noah nearly activated Plot Armor to achieve a state of invincibility, but he held it off.

This wasn't a life and death situation, and as much as the Sword Emperor was thrashing him around, he didn't actually want to kill him.

This could be seen by how he was freely talking while throwing out his palms, and also why he wasn't throwing these powerful attacks to Noah's summons as the Sage targeted him alone!