@3RDp I would rather not make assumptions on what he thought based on the dude simply asking his messed up kid if he is doing alright.
I guess in simpler terms we could say the dad is at fault for being naive and complacient with the ideal lifestyle of a average japanese household. But that is hardly anything worth taking responsability out of Seiko, which is what I'm having an issue with: All those comments whining about why he didnt do anything, when the one responsable for the abuse is the mother are baffling. I get that we dont know exactly how much he knew, and therefore we assume he knew Seiko tried to kill their child like 5 times or some shit, but also
because of the social context, it would be hard for the issue to simply end with a divorce or anything other than trying to keep it inside the family without involving "outsiders".
Personally, I think If Seiichi happened to snap at his dad, It wont be for the reasons you think, but because he is a tormented child that most likely wont have the tools to handle and properly cope with the abuse inflicted by his own mother. In cases like that, and assuming the mom will be out the picture, children like Seiichi tend to redirect their feelings to the next thing around them, regardless of said person being supportive or not. Seiichi (speculating here, just pointing that out) in that hypothetical case, would blame his dad not because he really believes he is to blame for the sins of his mother, but because he cant get the closure he needs. Or maybe he is going to be emotionally dead for a while, idk.
Anyways this manga is interesting in a morbid sense. Cant wait to see how it ends but im half expecting an average ending/nothing out the ordinary