Ishiyama High School, known for its tough delinquents, is where first-year student Tatsumi Oga, nicknamed the 'Demon King,' reigns supreme after defeating many foes. One day, after a brawl, Oga discovers an infant whom he reluctantly decides to look after. The baby, revealed to be Kaiser de Emperana Beelzebub IV, becomes inexplicably attached to Oga. Tasked with raising the child by a demon maid, Oga faces the challenge of caring for Baby Beel, who has the power to cause harm if Oga strays too far. Juggling his delinquent lifestyle with unexpected fatherhood, Oga navigates a world of demons, hostile peers, and his unconventional role as a caregiver to Baby Beel.