Millennium Research Institute, a counseling office where bizarre requests come in. The head of the research institute, Ichirō Umoregi, also known as "Akuma-kun," a genius boy who only appears once in 10,000 years. However, he doesn't know his real family. So Akuma-kun, along with his partner Mephisto III, pursue the mystery of his origin while challenging mysterious cases in this mysterious detective buddy story.