Ishiyama High—land of the delinquents. No matter how tough you think you are, you don't mess with an Ishi-high student. One of the most infamous students is first year Tatsumi Oga, called "Demon King" by those he's defeated. One day, while Oga is finishing off a gang that attacked him, he stumbles upon an infant. In a rare moment of kindness, Oga tries to care for the baby. As a result, the child becomes overly attached to him. In a panic, he brings the baby to his best friend Takayuki Furuichi's house. While there, they are attacked by Hildegard, a demon maid who says the baby is actually Kaiser de Emperana Beelzebub IV. She also reveals that he was sent here to destroy humanity, on a whim of his father Beelzebub III, Great Demon Lord of the Demon World. After failing to remove Baby Bee