Small But Mighty Demon King.

Aeternus doesn't plan to kill the Celestial supreme on this trip to the divine plane. He has more modest objectives. A lot has changed since they last met, he is here to see if the changes that Legion has undergone will affect the Celestial Supreme in any way. 

He is the only one that can do it since Helios is no more in the plane and the tree father's avatar can't move. He will just collect some data on the god of fate for Legion and be on his way.

He found the Celestial Supreme sitting above the divine city. The god of fate has numerous screens opened and showing various scenes of the mortal realm. He is content with sitting and watching the events of the plane without interfering whatsoever.

The god of fate asked him without turning to look at him. "I noticed that the officers of your army are returning to the abyss. It seems your job on this plane is done. Are you here to say goodbye?"