When Ren saw the being that suddenly appeared before him, he could identify the other party almost instantly. This was the one most high, the absolute ruler of the endless universes, the controller of all laws between heaven and earth, supreme and unparalleled. The Omnipotent, the Omniscient, the Omnipresent, the ORIGIN.
The body of the ORIGIN looks like it was made up of multiple universes swirling within his deep abyss-like body. Just looking at the body of the ORIGIN makes one feel the vastness of the universe, it would make one feel the very breath of the universe.
Just simply standing in front of him, Ren could feel a sense of oppression that penetrated his very soul, but as a reincarnation of the Strongest Mortal Soul he could resist it, if it were anyone else they would've already knelt or if they were weaker died by simply being in the presence of the ORIGIN.