The Nirvana Martial Contest, she must win!
The rewards for the first place, she must obtain!
Not only must she win, but she must win honorably!
Not only must she obtain it, but she must obtain it rightfully, leaving no grounds for reproach!
In other words, having guessed the true intentions of the Hidden World Clan, Gu Changsheng considered that if she exposed the identity of the Southern Emperor, given the Hidden World Clan's nature of compromising for their purposes, the first place position would likely become a sure thing for Gu Changsheng. Even in the unlikely event that Gu Changsheng was truly outmatched by those talented young ones, the Hidden World Clan might hand over the first place position to her to establish good relations for the future with her, the Empress holding most of the realm!
But then, what would be the point for her, Gu Changsheng, to bind her Inner Strength and participate in this Nirvana Martial Contest?
