Chang Ming Hui, often referred to as Mr. Chang or simply Chang, is one of the secondary characters in Detention. He is the school guidance counselor, and helped Ray get her academics back on track when she was having trouble at home.
Chang believes in the idea that people are born to live freely, and to create and share their own ideas without restriction or fear. He helped to discreetly supply the book club with banned books, until Ray leaked the list to Instructor Bai, who then had him, Yin and all the students in the book club arrested. Chang was found guilty and was executed.
During Ray's counseling, the two grew close to each other and had a brief romantic relationship. When Ms. Yin confronts him about what's going on between the two of them, he cuts Ray off and distances himself from her.
It is implied, but not directly stated, that he may have had a romantic relationship with Ms. Yin.
Chang is already dead during the events of the game, so his presence is limited to flashbacks. Chang's relationship with Ray is the focus of Chapter 3.