The story follows Oga Tatsumi, a first year in Ishiyama High, who has been chosen to raise a baby boy, Beelzebub (aka Beel or Berebo), who is the son of the great demon king, along with the baby's maid Hilda. As Oga attempts to 'pass on' Baby Beel to other stronger students at Ishiyama High, he crosses paths with the Touhoushinki (Ishiyama's strongest four)and their story ensues.

Source: Wikipedia