Oga has been chosen to be the parent of Beelzebub, the son of the Great Demon Lord. However Oga's suffering since every time Baby Beel cries he lets out a severe electric shock. Plus, according to Baby Beel's demon maidservant Hildegarde (Hilda), if Baby Beel moves farther than 15 meters away from his human parent Oga, the electric shock will reach lethal levels. Oga shuffles to school with Baby Beel clinging to his back, having no other choice, and begins to search for someone even stronger than him that Baby Beel will take a liking to, in order to get this monkey off his back, literally!

Oga Tatsumi is a crazy-strong, ruthless high school delinquent who's nicknamed the "Rampaging Ogre". One day, while dunking some punk, he rescues a big guy who comes ~floating~ down the river. When he does, the big guy splits in half and out pops a bouncing baby boy! But this baby is actually Kaiser de Emperana Beelzebub IV (Baby Beel), the son of the Great Demon Lord, and he came from the Demon World in order to destroy humanity!