August…actually wasn't as perturbed by the news as Damien originally expected him to be.
It was definitely troubling for him to realize that he had been born for a specific reason. The burden of his ancestor's dying wish was a hard one to carry.
But…
While he did respect the Azure Dragon, he wasn't willing to give up his life for his dream. His ancestor was worthy of his respect, but not his fealty.
Obviously, the fact that Damien cared about his ancestor's goal was the most important factor. That made August take it into serious consideration, and more than that, the reason why he was fine with doing as his ancestor pleased was…
'...that was my goal from the start.'
He heard tales of the Dragon Emperor when Damien took him to the town. He wanted to be that person who could stand above a million dragons, and he wanted to be the shield that protected them from harm.
The only thing Qinglong's story changed was context.