It's a horror manga honestly, it was a messed up story but i kinda wanna see it to the end. A guy was transferred to an orphanage (if i'm not mistaken) where he would be a new teacher (??) But then he found out the kids there were not normal because they do gory work. This orphanage was actually a human disposal place and the one doing the killing were the kids. Some defect yakuzas, criminals, etc were sent here to get killed. Then there was a plot twist where the guy transferred here was actually a former member of this so called orphanage.
It's the master servent story. Master has a sign on his hands as well as the servent on the back of his neck.
http://www.mangago.me/read-manga/royal_servant/ ... perhaps
I really wanted to read this manga but because of the stupid f******* author I can't read this anymore ヽ(`Д´)ノ (︶︿︶)=凸 (/TДT)/ ┑( ̄Д  ̄)┍