Yuffie was, had been and would be two things her entire life. A princess and a thief.
Yufffie had always known she was a princess, even if she wasn't a princess like in the stories that her nursemaid read to her. In the stories, princesses always had long, blond hair, blue eyes, a big castle, and, most importantly, the princesses didn't do anything until they were saved by 'Prince Charming.'
Yuffie found these books deeply unsatisfying.
After all, Yuffie was still a princess, even though she had short black hair, light brown eyes, and lived in a country that had been at war long before she was born. Yuffie was still a princess, and she always would be. But she wasn't like the other princesses, the princesses in stories (Yuffie wasn't even sure if princesses like that were real). Yuffie was strong. She was smart. And she could fight for herself. Yes, Yuffie would always be a princess, she would just be a different kind of princess. And she continued to be a princess until the day she died. That wasn't true for the second part of her.
However, Yuffie hadn't been born a thief. Looking back, she had become a thief completely by accident. At first, stealing had just been a game. You look something, hid it from whomever you'd stolen it from, and then, a couple weeks later, you put whatever you'd stolen back.
Yuffie was eight when she first realized that stealing could be of some use. She could steal treasures, and give them to her beloved Wutai. Said treasures could then be sold for money, and money was always a big help in this never-ending war against ShinRa. And, of course, Yuffie, Princess of the Thieves had a nice ring to it. Someday, she hoped, people would know her name. Yuffie, the Princess of Wutai, the Master Ninja, and the Amazing Thief.
At first, when she went to Midgar, Yuffie had no interest in men. All they did was slow her down, and get in her way. They wanted to take the claim for finding treasure. Yuffie hated that. Besides, men were just plain nasty; they couldn't keep their hands to themselves. The first lesson about Midgar that Yuffie learned (even before she learned that you shouldn't keep what you steal in plain sight.) was that you should never, ever, ever leave the safety of wherever you were staying without some sort of means to defend yourself by. After learning this, Yuffie never left Seventh Heaven without her shuriken, not even to buy a bottle of water.
When she had first met Vincent, he had terrified her. They were complete opposites. Yuffie was bubbly, loud, and clumsy. Vincent was silent, quiet and not clumsy. But as they were both on the 'We've got to save the world' team, they did have to talk to each other. So their conversations started out as polite, nothing more than two teammates talking. Then, when they began to know (and understand) each other a little bit more, their conversations become a little more than just forced polite; though it was hard to have a conversation with Vincent that wasn't polite and to the point.
Yuffie couldn't exactly pin-point when she had started falling in love with Vincent. Nor did she know when he had started feeling the same way towards her. But she could tell you, with obvious pride, the first time they had kissed. And...many other things after.
And at first, Yuffie fooled herself into thinking this might actually work.
She was a fighter, and settling down to raise a brood of children was NOT part of Yuffie's grand scheme to rule the world. If any other man had asked this from her, Yuffie would have slapped them. But if Vincent had asked this of her, she would have dropped everything and gotten knocked up faster than you can say yes.
He never did.
Because all too soon, that little bitch Shelke came along. And screwed everything up. Because somehow, magically, stupidly, scientifically, she was Vincent's first love, Lucretia, reborn. Yuffie didn't regret slapping Shelke across the face. She didn't regret a single mean, or unkind thing she had done towards the girl. Because Shelke deserved it.
And Yuffie desperately tried to cling to her relationship with Vincent. She was the one for him, not Shelke. But apparently, Vincent didn't think so. Because in a matter of days, their relationship was flying backwards, to the point where they were just two colleagues talking to each other. No more kisses, no more kind words. Nothing.
Yuffie racked her brain trying to figure out what she had done wrong. She had stolen Vincent's heart. They had been together. Wasn't she pretty enough? Strong enough? What did Shelke have that Yuffie didn't?
Then it hit her. For the first time in her life, Yuffie hadn't stolen something. Or rather, Yuffie had stolen something that wasn't hers, and would never be hers. She had merely borrowed Vincent's heart, though it had first appeared as though she had stolen it. Yuffie had been like a cheap, second class weapon that you used until you could find your old one. She may have been a Princess of Thieves, but she had failed to steal the one thing she would have given her life to get. Vincent Valentine's affection.
Vincent would rather have some messed-up, four times younger than him little science project who was really his one and true love reborn. And Yuffie did her best to accept that. Even though it was like tearing out her own heart with a dull throwing needle, Yuffie pretended not to care. She went through life bubbly, stupid, clusmy and kind. Only those who really knew her saw that flicker of regret in her eyes. Only those who really knew her saw that Yufffie had truly grown up.
His heart was the last thing Yuffie ever stole. For she may have been a princess and she would always be a princess, but after nine years of stealing and taking, Yuffie stopped being a thief.