Listen..Enji and Rei were shitty as a collective. Neither of them were good parents, Enji may have created the shitty path but Rei definitely walked by herself. This is not to take any hate away from Enji because I do think he was a terrible parent, but Rei was no better. They both raised the anger, hateful boy that is Touya.
This is my second time reading and I still love it!! But you can’t say that the main couple and second couple were given the same amount of attention. Even chapter wise, the second couple took up a fuck ton of the story and even had a longer epilogue compared to the actual main couple. So I’m not saying the story was bad, it’s just weird
My feeling that I get out of this is that the author understood or had a clear vision of the second couple than she did the first couple. And that's why she really took it further with the second couple.