Koakuma Kyoushi Psycho summary:

A captivating new teacher, Miss Kasai, arrives at a troubled classroom. The previous teacher had been hospitalized after a tragic attempt at self-harm, driven to despair by student bullying. "My goal as a teacher is to bring joy to my students," she says with a laugh, before turning her attention to addressing the bullies in her own unique way. However, the students are about to discover that Miss Kasai is not to be underestimated. Could Miss Kasai be hiding a darker side?