Vast Sun Sky Guqin

In fact, never mind the rest of the soul masters' organizations, not even everyone in the War God Hall was aware of the Vast Sun Douluo and the Demon Guqin Douluo's martial soul fusion skill. 

This was also the reason why the Boundless Sea Douluo Chen Xinjie had already decided that Ao Rui would become the War God Hall's Hall Master after Gan Yue. 

Any soul masters' organization would need to have an elite warrior to assume personal command over it. Otherwise, the organization would be pressured by others into yielding just as the Spirit Pagoda was pressured by Shrek Academy in the past. 

The name of this martial soul fusion skill was the Vast Sun Sky Guqin. The Guqin's strings were being plucked despite having no one playing it.