when it comes to the daughter, MC does not deserve any forgiveness. Sure her running away was stupid, but that was the worst she ever did. Meanwhile, he's basically neglected her for most her teen life, especially after the mother died... then he literally abandoned her on the side of the road to chase after his creepy ass "love" -_-
gross is actually quite a kind word from the daughter, she could do so much worse based on his actions. I'll link a comment from reddit that sums it up nicely from this side of the story and MC being a terrible parent and adult:
He pretty much never around when she was a kid. He was too busy with work even while his wife was on her deathbed. He was busy with work after she died as well and didn't take the chance to reconnect with her. This other side she speaks of is the side of him that is chasing after a teenage girl, a girl at the same age as her. Of course, she would think that's gross.
And then she cries her eyes out and begs him to stay, and yet he still doesn't think she's important enough. In addition to all of this, you have to remember that she is still just a fucking kid. She was 13 when her mother and even younger when her father stopped paying attention to her family. She has every right to be mad at him
if things get too tough, abandoning your child is never the correct option. Either you get professional help yourself to manage your life, or you get someone to help take care of your child.
and then from Koto side of things, putting aside the holy yikes creep and pedo, he knows of the real issues Koto has with her home and parents: father abandonment, hence her seeking our adult males = father figures, to her issues with the mom
yet he does nothing as an adult should do when they find a troubled child like this :/ didn't even get her some professional help to talk with cause he was too busy not rejecting her advances and being a creep
like holy hell, she almost got raped and he didn't even care to do anything for that, too busy going "here's my creepy love". Also she's not 18 (age of consent in Tokyo) = she can't make a decision about being with him, even if it's waiting as that's the point of age of consent. He would need the mother's approval and she flat out said no