The Two Jiaos of Mt. Huai, within the world of wandering cultivators, although not as renowned as the six great titans, held a significant status. Would they have sold their lives for Emperor Pillzenith if they hadn't been compromised by something he held over them? Moreover, Emperor Pillzenith had assured them that this mission would be easy; all they needed to do was follow Great Emperor Asura, heed his commands, and slay the young master of Veluriyam Capital.
Once the deed was done, their grudges with Emperor Pillzenith would be settled in one stroke, leaving them indebted to no one.
In order to escape the entanglement of Emperor Pillzenith and to clear the air of indebtedness, that's why the Two Jiaos of Mt. Huai had agreed to the assassination.
