Your subjects finally came back with the man you think responsible for the change. You ponder for moment how to proceed, before deciding to interrogate him. At first, he refuse to say his name and pretend he spoke of another, unrelated matter. But regardless of how good he is a lying, as a demoness you can feel he isn't telling the truth, and so do your subjects.
Using your powers, you make him fall so profoundly in love with you that he won't even think of telling you anything but the truth. The better part being that you let him know it was because of your powers, which terrified him. But even the terror of knowing how artificial where his feelings for you couldn't diminish his new found willingness to tell the truth.
“I'm part of the few peoples realizing how humanity is destroying everything, how every other living beings would be better of without humans. On of our solution was call demons to Earth, making them exterminate that parasite called humanity. Alas, it seems to only be a partial success…”
Distraught by that revelation, you aren't sure what to do with him…