I like how dad here was written. He didn't just immediately fold the moment she called him "dad", but he wasn't being a jerk for no reason. Anyone would be confused and/or irritated like him if they had to suddenly take care of their sibling's kid with no explanation or financial support, or even a time frame. And yet he took the responsibility of raising her seriously in the end.
I guess I'm just used to sloppy writing in manga at this point, but this one keeps positively surprising me every time.