People be hating on the dad for being neglectful and ignorant and I definitely agree but I don't think he is to blame. Some people just have no idea how to deal with a situation like this and don't know what to say so they end up saying... Nothing. It's shitty but it is definitely a human way to react especially when you didn't know what was going on the entire time because, let's face it, Seiko is a sociopath and she's a terrifyingly good one at that. This kind of 'mental paralysis' is real, it's human. It's not that he doesn't care, he just has no clue what to do with his son.