As an existence of the Sky-Reaching Realm, it's extremely difficult to submit to someone, but back in Ancient Times, a few who were of the Sky-Reaching Realm either died by the hands of the Demon Race, the rest either submitted to the Emperor of Mankind or, like the Great Celestial Demon Lord, they could only be killed.
However, whether it's Buddha or Taoist Ancestor, even the Emperor of Mankind himself knows that people like Taoist Ancestor and Buddha would not easily submit. Nevertheless, the Emperor of Mankind dares to have them under his command because he is confident that, with his own strength, Buddha and Taoist Ancestor won't dare to try any trickery.
Moreover, Buddha and Taoist Ancestor have ceased the intention to compete with the Emperor of Mankind in this era. Instead, they are secretly observing the Emperor of Mankind, seeking to understand him and find his weaknesses.
