Ishi Middle School’s legendary no-loss Oga Tatsumi-kun is a fierce young man who can beat dozens of people without sweating. He was sleeping near the river while some enemies try taking taking chance beating him. They end tragically. at that moment, Oga caught an old man floating on the river. He pulled the old man ashore and suddenly the body splitted into two. From within, there’s a baby boy who soon attach to Oga for his fierce look.
As Oga tells this to his best friend, Furuichi, a young woman steps in from Furuichi’s window. Her name is Hildegard, comes from Hell as caretaker of the baby. She claims the baby as demond king.