It's a fantasy/horror/fighting manga.
The protagonist goes to this school surrounded with a giant wall, which is for people with sort of weird powers.
Overtime, he develops a power, which is basically a 'mole' on his face but is super strong and can help him regenerate limbs and do stuff, etc.
There is also a girl who is with him all the time. From what I remember, she wears glasses, is quite quiet to begin with and fights with a katana/sword.
If any of you can tell me what this manga is, it would be great as I would like to read it again.