What is justice, and what is evil...? Japan has suddenly fallen into an extreme situation, and behind the chaos is a group of mysterious invaders, called the Septentriones, who are flinging the entire nation into the depths of despair! Is this a test for the human race? As this epic, cruel reality continues to trifle with the people, thirteen individuals with unique characteristics form contracts with demons to become the "Devil Summoners," giving them the power to fight the invaders. This is the story of the conflicts and discord faced by the many people caught in this extreme situation.