I don’t know why, but for some reason I have a thing against romantic interests who are introduced more than halfway through a series. And even more so I can’t stand when that romantic interest gets so much of a fan following (especially when I know that said romantic interest is a goner anyway). I don’t know why, but it just bugs me. I guess it’s because by that point I’m already invested in another pairing, usually with a character that has been around for much longer.
Well, not much I can do about that, it’s just how I feel. But for anyone reading this that is thinking of writing a series of any kind, please don’t make the mistake of introducing any permanent, or final love interest when your story is already well under way. If you’re going to have a character like that, introduce her (or him, I’m looking at you Yabuki, and you Oh-Great!) at the start of the series. Otherwise fans will get attached to other characters, and dislike the actual romantic interest.
Then again, I could be wrong, seeing how much fan support characters like Luciolla and Boa Hancock seem to get (ship jumping traitors!!!). So it might just be me. So consider this a way to please me in your writing. But in all honesty I think this is a pretty decent rule that it can’t hurt to follow.