The story revolves around Oga Tatsumi, a strong juvenile delinquent at Ishiyama High. One day, he encounters a man floating down the river who splits in half, revealing a baby boy who bursts into electricity whenever he is upset. He soon learns from the child's wetnurse, Hildegarde, that this baby is Kaiser de Emperana Beelzebub IV (Baby Beel for short), the son of the Demon King who has been sent to the human world in order to destroy it. Oga soon unwillingly finds himself in the position of being Baby Beel's human parent to train him to destroy humanity. Thus begins Oga's life as the parent of a demon