From Mana, to Neko Musume, and later to Kitaro and Medama Oyaji. They finally know what happened in the human world and the youkai that causes this. Medama Oyaji also adds about how Ama-no-Jaku is a twisted youkai who loves creating misfortunes for his own amusement.
So Okuda meets Nezumi Otoko, and both of them encounter the youkai Ama-no-Jaku. This youkai despises humans' happiness, and they want to make a show about making people unhappy and laugh at it.