At the end of the second semester of third year of high school, four students are prepared for graduation and feel the ending to their high school life. But that changes a little with the arrival of a transfer student.

Professional wrestler and animal lover Shibata Genzo is suddenly summoned to another world. Greeted by a princess, she requests to get rid of the evil beasts roaming in this world. Outraged that he was asked to kill monsters, Genzo German suplexes the princess. Unable back to get back to Earth, he decides to live a peaceful life and manage a "monster" pet shop.

Competitive sharpshooter Hikari Kokura hopes to join the Chidori High School light-beam rifle shooting club — but the club has been disbanded! If she wants to hone her skills, she'll have to recruit fellow students and save the club!

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.