You’re Doing This On Purpose

If Heavenspan Island was the imperial palace, and the Celestial was the emperor, then the demigod patriarchs from the riversource sects would be analogous to the four heavenly kings, such as the Giant Ghost King.

As such, Bai Xiaochun and Master Cloud Lightning were like two powerful subordinates of two heavenly kings. Although they were technically on the same side, in truth... there was enough tension between them to lead to deadly conflict. On the outside, the demigod patriarchs would ensure that their followers didn't get into conflicts such as the current one.

But inside a trial by fire like this, where deaths were expected, then even if one killed the other, they could easily explain it away after leaving.

Master Cloud Lightning had been forced to simply watch as Bai Xiaochun pushed his other half to near destruction. Then, that same person went on to personally kill his apprentice.