Kagi no Nai Torikago

Haru is depressed after accidentally overhearing her friends true thoughts about her. One of teachers realizes this and comforts her. At first he seems like a kind and nice counselor but their relationship escalates quickly as the teacher reveals his hidden self. Haru decides to stick to this teacher but at the time she did not know just how deep the teachers darkness really was...

(Source: MU)