It’s not that confusing. He did get adopted by a different person but he never forgot the mental abuse he went through when he was with the main characters’ family. He always wanted his revenge but the parents of the main character passed away even before he could do anything. He lost all the hope. He for some reason did not want to hurt the older brother so instead he chose a new target (younger sister) to get his revenge. Or maybe it would be more easy to manipulate a child. That’s all there is. He was revenge hungry but in the end he couldn’t hurt the brother. He never thought the girl would kill herself. He just wanted to alienate her from her brother and just mentally torture her.
Honestly I dont understand the blond guy's problem like why did he take it out on the girl and the guy and wtf so he is the half uncle of 0941 and afk but he got adopted by a different man like wtf??? Its all just too confusing somebody please explain