Noah's darkness had halved after his last attack. Sword Saint's lunge was a technique that he shouldn't perform recklessly before mastering it.
That wasn't one of Noah's casual slashes. It was part of Sword Saint's core inheritance. The energy that it depleted even surpassed the requirements of the Demonic Form.
Yet, the power that it was able to unleash made up for that consumption. Noah had launched a lunge that even peak gaseous stage powerhouses would struggle to block while he was still a rank 5 cultivator!
The Royals couldn't explain that event. Their prison was one of the last items created by their Father, but Noah had pierced right through it without even activating his iconic Demonic Form.
Their battle intent waned at that sight. They didn't have stronger methods to fight him there, and Noah overcame them without relying on spells.