Anerias left after hammering out the details of their deal. He would lure monsters close to the campus every three days for two months in exchange for the information Zach had given him about how to help his Blackfire Hound grow stronger. It seemed unfair. All Zach had to do was open his mouth a little. Anerias, on the other hand, had to risk his life and work like a dog to attract monsters.
But while Zach and the others would only get a limited boost to their levels from what he could bring, Anerias had found the stairway leading upward for his familiar. The immediate gains were out of balance in consideration of the future benefits.
Of course, if Zach wanted more, he could always poke Anerias and share some more information, such as what creatures were from Heaven or Hell, where he could find them, and the part about a familiar's evolution.