I think the brother was made this attractive on purpose because we are not meant to hate him right away, if he were only the slightest bit less handsome would we still be rooting for him even though we have been shown how cruel and evil he truly is? It is because of his attractiveness that we are still able to feel empathy for him, kind of like Sanwgoo from Killing Stalking who gets a lot of free moral passes just because he is *extremely hot* and had a tragic backstory. Despite the fact that he is a serial killer people still cheered for him an wanted him to redeem himself to the very last moment, the fact that in the end even his whole body was marred and destroyed was meant to make him lose even one of his last redeeming points in the eyes of the viewer to emphasize that there's no excuse for murder and nobody is exempt from the laws and karma.
I think the brother was made this attractive on purpose because we are not meant to hate him right away, if he were only the slightest bit less handsome would we still be rooting for him even though we have been shown how cruel and evil he truly is? It is because of his attractiveness that we are still able to feel empathy for him, kind of like Sanwgoo from Killing Stalking who gets a lot of free moral passes just because he is *extremely hot* and had a tragic backstory. Despite the fact that he is a serial killer people still cheered for him an wanted him to redeem himself to the very last moment, the fact that in the end even his whole body was marred and destroyed was meant to make him lose even one of his last redeeming points in the eyes of the viewer to emphasize that there's no excuse for murder and nobody is exempt from the laws and karma.