With Sea Change, I headcanon that while Hatori looks like Oikawa, that Y/n's daughter looks exactly like her.

Also, because Oikawa views his children in the lense that they should act the perfect children, how would he react if his daughter grew up, saw how fucked the whole family dynamic was and started rebelling and disrespecting him??

hmmm for certain iterations of oikawa, that'd be true. scion oikawa would very much be a ruthless parent, settle/sea change kawa's a little more chill, the love he's got for his kids is genuine and unconditional.

i actually think hatori, being the oldest and the mama's boy that he is, would be the one to act out. tooru's not pleased in the slightest, although i do think there's some small part of him that's almost... proud, maybe, that his son's standing up for her. doesn't make him any less irritated by it, but at least it's coming from a good place?

ultimately he's not gonna hurt either one of his kids. full stop. he'll get frustrated and pissy, and depending on how old they are, he might threaten to cut them off and/or make it so they can't see her, but that's pretty much it