You'd Better Listen to the Revelations from the Gods

The gods told me that humanity will perish. He told me again that I could save everything. I gained the ability to find the murderer, but—— I looked at the boy in front of me who was the same age as me but 14cm tall and had a handsome face, and fell into deep thought. Are you the great devil who exterminates mankind? My deskmate! Well, I would like to ask you a question. For the sake of us having sat at the same table for six years and being good friends for ten years, please answer truthfully - you are not planning to kill all human beings, are you?