I don't think either of them are too good for one another. Neither one was truly good or evil in my opinion. They just had different goals which clashed with each other. Sure Kuni wanted to steal Yoshi's sword, but she wanted it to please her dieing grandfather. Her main fault is greed, wanting to keep things for herself. I doubt she'd ever do something as unforgivable as Bryan did.
The main problem with a romance is they are both too proud. They'd never admit any feels for each other.