atsushi's parents would definitely not be happy to react to their "son". they would most likely be uninterested and/or be upset by the sight of him. their past relationship with atsushi is not fully known, all that is known is that they were not good parents at all, and did things much worse compared to what the orphanage directed did. NO HATE!! JUST LETTING YOU KNOW :)
its not canon, we actually dont have informations on his parents. But, the headmaster did say one time that his parents did something more aweful to him. But he could've lied and his parents just abandoned him