Battle Royal High School is the English name of Shinmajinden Batoru
Royaru Haisukuru, a Japanese comic and the 60 minutes long animated
special based on the comic. It details the resultant confusion when the
best fighter in a Japanese high school's karate club chooses to quit
school and become a professional fighter. His choice fulfills an ancient
prophecy that marks him as the demon overlord of the world, making the
high school a battleground as demons, exorcists, and even law
enforcement descends upon him.