Seven Mortal Sins
The prideful archangel Lucifer disobeys God and is cast into the lowest level of hell as a fallen angel. On her way to hell, Lucifer happens to meet a high school girl on Earth named Maria, who helps her. In hell, Lucifer meets Leviathan, and Leviathan explains to Lucifer about The Seven Deadly Sins, the seven demon king rulers of hell. After The Seven Deadly Sins seal Lucifer's powers, Lucifer goes on a journey with Maria and Leviathan to defeat them.
The Proud Fallen Angel
Totsuka Maria was praying in a chapel at Seiseki Girls' Academy when a black cross comes falling from the sky. On that cross, was a fallen angel, bearing the sin of pride, Lucifer. Maria attempt to tend to the angel, but the floor falls out and she disappears. Lucifer finds herself in the depths of hell, and runs into the Demon Lord of Envy, Leviathan.
