Looting And Pillaging.
The spell isn't shiny like that Niva the beholder produced. It was dark and ominous like something a god of death will produce, but the power of the beam he fired overwhelmed the beam that Niva produced and destroyed its producer too. The fallout from the clashing of the explosion also took the lives of the blade demoness and the scorpion demon of weakness. They were at the wrong place at the right time for them to become collateral damage.
Aeternus's vision was extended as he watched the beam of light warp from this location to numerous ones chasing after Niva the beholder. It seemed that the Niva that he fought was a clone of a large network but the beam was intent on killing every one of them. It struck each of these clones no matter where they were, underneath the ground or behind heavy defenses, and erased their souls. The beam was unrelenting in its efforts to fulfill its aim of eradicating its target.