Searching a Anime name

Hey I'm looking for the title of an anime that I watched a few years ago.

Maybe someone knows it so that's the info I remember:

So it was about a student who was in an academy? I think Who had no feelings I think And was very strong when he turned unintentionally His transformation look was green more like a zombie When he turned the teachers made a shield around him which but also always almost went broken because he was too strong , I Think there was a girl too that helped him to get normal.

I do not know the best explanation but maybe someone knows which one I mean