Letting himself loose
Roku was not the only one baffled by the destructive might that Zatiel's Nine x Nine Supernova Blast created. While a Rank 7 life form could provoke even greater destruction, they achieved that feat by depending on raw power and not on their supernatural abilities.
It is like comparing the destructive might of 20 tons of TNT with a small nuclear weapon. While both could theoretically provoke the same damage, there was no question on which one was superior in their efficiency and nature.
A Gods' Hero named Markus could not take his eyes away from the area where nothing but emptiness remained. He trained the Law of Destruction but knew that even if he sacrificed all, he would never be capable of such a feat.
Unfortunately for Markus, his lapse of concentration cost him dearly, as the Astral Fiend appeared before him without realizing it.