Even after killing Sylvius, Damien didn't stop. His original goal was to psychologically attack the enemies with a show of strength, but his unfamiliarity with his own power disallowed this circumstance from becoming reality.
Now that the battle had ended, he needed to accomplish that original purpose. And along with that, he needed to find better test dummies to help him understand his strength before he challenged people above his level.
Damien's targets were now those on the weaker side of things, at similar levels to him. Against them, he wouldn't have to worry about the prospect of losing. He would be able to thoroughly understand at least how to utilize his Void Mana's suppression effect properly.