Freshly cast out of Heaven, the former angel Lucifer makes a brief stop in a high school church on Earth, where she encounters a girl named Maria Totsuka before continuing her fall to Hell. Once there, she is met and fawned over by Leviathan, an aspiring minor Demon Lord, and challenged to combat by Satan and Belial, two Demon Lords of the Seven Mortal Sins and members of the ruling council of Hell who accuse her of intending an invasion of their territory...