Responses
It's rather clear that he's abroad, I think. Once her brother returned, she might wish to see her dad, too. If he's still alive. And since she didn't contact Ai in all those years, one can only speculate if Ai told their father of her. Fro what her mother reports, it's pretty clear that he cannot know otherwise.
but if they have the same dad why doesn't mashiro also meet him?
does he know he has a daughter?