While I don't read Harry Potter fanfic, I do read fanfic for other series, and this essentially has 'underage female slave fanfic that ends in sex' written all over it. Though one does wonder what their reaction would have been had the slave been a young boy, and the 'owner' a slightly older girl. Both ideas squick the hell out of me, but then, I prefer my sex to be between consensual adults. So what do I know?