The story takes place in Tokyo Butei High School, a special school where armed detectives — "Butei" — are trained to use weapons. Kinji Tooyama is a second-year-student who has a special ability, but he keeps it a secret to maintain an ordinary, peaceful life. However, when he gets caught in a bombing on the way to school, he encounters H. Aria Kanzaki, the most powerful S-Rank Butei student in Assault Studies.
Most animes have no backing for their story. Hidan no Aria succesfully incorporates common knowledge myths and history to create an anime that seems to flow with society itself. Each of the main characters in the anime have an eventful ancestral history. Great stuff. An anime that actually makes sense.