This is the story about Zero which was born physically different from others. Growing up in an environment where all the same and you are different isn't that easy. In this story, Zero is passing through hard childhood just because he is different from others and it seems that everyone in his environment is too evil to like him.

But as it always tends to be for those who are strong enough to bear all the troubles they are facing, even Zero finds his happy end. He finds his friend and his love which is same like him and, despite all difficulties they are facing, they still managed to find a path to happiness. [source]