In face of human technological advancement during the Meiji Restoration, the youkai of Japan were forced to make a hard decision:
1) To remain as youkai and watch over the land. 2) To return to the netherworld. 3) To give up their power and status as youkai and live amongst humans. While there were some that chose otherwise, the majority of the youkai decided it was best to become human. It was tough, but as time passed these youkai were able to blend in with the human world and live peacefully amongst them. However, blood is thicker than water. The offspring of these youkai displayed the powerful abilities of their ancestors in times of great anxiety, often manifesting in horrible and dangerous ways, and were labeled by society as monsters.