To be honest, even a ruler of a high-level hell plane was not without weaknesses.
That was, once it left its high-level hell plane and lost the augmentation of that plane's origin power, its strength would rapidly weaken and return to its original combat power.
But as the ruler of a plane, it was an invincible existence while remaining within its own plane. Even invincible demons could be effortlessly suppressed, utterly unable to fight back.
Had they known this earlier, they definitely would not have stupidly stayed in Green Lotus Hell to fight Xia Ping. They would have fled Green Lotus Hell long ago.
In fact, once a high-level hell plane had a ruler, all other invincible demons would immediately flee. They would never stay behind and wait to die.
Unless an invincible demon was willing to submit to such a plane ruler and willingly acknowledge the other party as its master.
There were actually quite a few invincible demons like that.
After all, Hell was still filled with vast numbers of terrifying Void Monsters. These Void Monsters slaughtered everywhere; even invincible demons could not withstand them and would be devoured completely.
But if a high-level hell plane had a ruler, that would greatly enhance the plane's offensive and defensive power, turning it into an extremely safe fortress.
Thus, in order to preserve their lives and evade the pursuit of Void Monsters, these invincible demons were also willing to submit to the rule of a plane ruler.
Of course, there were also some invincible demons unwilling to bow beneath another. They simply fled.
Invincible demons such as Hell Elephants and Hell Hounds were exactly like this.
After all, everyone was a demon of the Invincible Realm. Why should you get to lord it over me, boss me around, and point