about looking for yaoi manga
I read it within the past year. It's about a teacher who gets assigned to this school with supernatural students. There's one student who bites or kisses the teacher and that 'marks' him. The student disappears because he's turning into this demonic creature.
It's similar to this manga:
http://www.mangago.me/read-manga/sensei_kowai_hanashi_shimasenka/
It's similar to this manga:
http://www.mangago.me/read-manga/sensei_kowai_hanashi_shimasenka/