A couple very different ideas.

[EdwardThatch]

Looking for a young lady for a story driven, romance oriented RP.  Heavy on the affection and light on the kinks.  I had thought something along the lines of a forced marriage.  Perhaps it to seal a peace treaty or her dad owes him a lot of money and so sent her to be his bride to pay it off.  He'll figure he'll have to teach his wife how to be noble and a good wife before she can be a proper wife.  She could come expecting to be fully a wife to him or she could be innocent and they discover each other together.

Or Another, more taboo idea.

Say her father, a trust fund type and last heir of the fortune had a regrettable night with a girl in college. Years later he learns that has a daughter and the mom is 1. dead 2. going to jail or 3. found to be unfit. So he has to come in and take custody of this little stranger. He's just to being a jet setter and playboy so she is a disruption and of course he don't know the first thing about how to be a dad or little girls at all. He knows plenty about grown girls so might try treating her that way