Urban: the Strongest in the World Is a High School Student?

In a world where humans and monsters coexist, monsters disguise themselves as humans and feed on humans. Human beings understand the rules of cultivating immortals and become Taoists to fight against it. After a long struggle, humans used rules to restrain the monsters. In order to maintain the rules, the "Demon Law Enforcement Bureau" was established to kill monsters that violated the rules. But... How come the strongest person in the executive bureau is a high school student? !!