In the 30th century A.D., in a world in which magic exists naturally, 100 years have passed since a great war between the human race and the Devil King. The war concluded with the human race's victory, even though there were many sacrifices. Slowly but surely civilizations began to rise again.

One day, a witch walks into a small town holding a newborn baby. Stopping in front of a church, she puts the baby in front of its door and then disappears. The church takes the baby in.

Ten years later, the baby named Sai Akuto ("Worst Evil") has grown into a child of the orphanage. He puts people in awe and perplexity with his virtuous preaching about love for and the equality of humanity. Akuto decides to live in modesty so as not to trouble others, and before long a family offers to adopt him.

However, on the day Akuto is to leave the orphanage, a new girl is brought in. She can't stop crying from loneliness, worrying the adults. Seeing this, Akuto decides to take all the money the orphanage gave him for his future living expenses and buy a hair ornament with a jewel on it. He hands it over to the girl promises that they'll meet again someday if she stops crying and takes good care of the ornament.

Five years later, Akuto passes the test to enter Constantin Magic High School and leaves his foster father's home. On the bus on his way to the school, he makes a new friend. But after they arrive at the school and undergo the vocational aptitude test, Akuto receives surprising results: "Examination Numbers: Number 021, Name: Sai Akuto. Future Occupation: the Devil King."