Devilish Reasoning

A young girl born into an aristocrat family was introduced to a boy about her age. The boy was devilish and intimidating. They were supposedly fiancee's but one day the girl disappeared. The young boy promised that he would find her. Years later the boy meets her again but she had changed completely, she wasn't the same. This didn't stop him. His goal now is to protect her and restore her to her original state.