Soshiste Akuma Wa Seigi Wo Kataru summary:

At Chesthill, a boys' school where the students are judged only for how right their acts are without regards for their wealth or birth, the top student is granted the position of “Angel”, head of the “Angel Council” who guides his fellow students to be right. Taiga, a teacher arrived from a country in the far east firmly believes in that which is right and aims to guide his students towards being right, but one student, Lucas, the black sheep of the school nicknamed “the devil” has other plans than going along with the ideals of rightness that the school embodies. After the Angel is murdered and Taiga is framed for the murder, he has no choice but to accept Lucas' offer to save him and follow the mad, coquettish Devil in his quest to solve the mystery of the Angel's murder and become the new Angel